Java programming-examples

Java Programming Examples
Find the best practical and ready to use Java Programming Examples.
Java runs on a variety of platforms, such as Windows, Mac OS, and the
various versions of UNIX.
These examples would be very useful for your projects and learning.
Java Basics Examples
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Example - Home
Example - Environment
Example - Strings
Example - Arrays
Example - Date & Time
Example - Methods
Example - Files
Example - Directories
Example - Exceptions
Example - Data Structure
Example - Collections
Example - Networking
Example - Threading
Example - Applets
Example - Simple GUI
Example - JDBC
Example - Regular Exp

Java Environment - Programming Examples
Learn how to play with Environment in Java programming. Here are most commonly used examples:
1.
2.
3.
4.
5.
6.
7.
8.
9.

How to compile a java file?
How to run a class file?
How to debug a java file?
How to set classpath?
How to view current classpath?
How to set destination of the class file?
How to run a compiled class file?
How to check version of java running on your system?
How to set classpath when class files are in .jar file?

Saikat Banerjee

Page 1

Problem Description:
How to compile a java file?

Solution:
Following example demonstrates how to compile a java file using javac command.
c:jdkdemoapp> javac First.java

Result:
The above code sample will produce the following result.
First.java compile successfully.

How to set multiple classpath?

Solution:
Following example demonstrates how to set multiple classpath. Multiple class paths are separated by a
semicolon.
c:> java -classpath C:javaMyClasse1;C:javaMyClass2
utility.testapp.main

Result:
Class path set.


Solution:
Following example demonstrates how to debug a java file using =g option with javac command.
c:> javac demo.java -g

Result:

Saikat Banerjee

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Demo.java will debug.

How to set classpath?

Solution:
Following example demonstrates how to set classpath.
C:> java -classpath C:javaDemoClasses utility.demoapp.main

Result:
Class path set.

How to view current classpath?

Solution:
Following example demonstrates how to view current classpath using echo command.
C:> echo %CLASSPATH%

Result:
.;C:Program FilesJavajre1.6.0_03libextQTJava.zip


Solution:
Following example demonstrates how to set destination of the class file that will be created after compiling a
java file using -d option with javac command.
c:> javac demo.java -d c:myclasses

Result:

Saikat Banerjee

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Demo application executed.

How to run a class file?

Solution:
Following example demonstrates how to run a class file from command prompt using java command.
c:jdkdemoapp>java First

Result:
Demo application executed.

How to check version of java running on your system?

Solution:
Following example demonstrates how to check version of java installed on your system using version argument
with java command.
java -version

Result:
java version "1.6.0_13"
Java(TM) SE Runtime Environment (build 1.6.0_13-b03)
Java HotSpot(TM) Client VM (build 11.3-b02, mixed mode, sharing)

How to set classpath when class files are in .jar file?

Solution:
Following example demonstrates how to set class path when classes are stored in a .jar or .zip file.
c:> java -classpath C:javamyclasses.jar utility.testapp.main

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Result:
Class path set.

Java String - Programming Examples
Learn how to play with strings in Java programming. Here are most commonly used examples:
1. How to compare strings?
2. How to search last occurance of a substring inside a substring?
3. How to remove a particular character from a string?
4. How to replace a substring inside a string by another one ?
5. How to reverse a String?
6. How to search a word inside a string?
7. How to split a string into a number of substrings ?
8. How to convert a string totally into upper case?
9. How to match regions in a string?
10. How to compare performance of two strings?
11. How to optimize string creation?
12. How to format strings?
13. How to concatenate two strings?
14. How to get unicode of strings?
15. How to buffer strings?

How to compare two strings ?

Solution:
Following example compares two strings by using str compareTo (string) , str compareToIgnoreCase(String)
and str compareTo(object string) of string class and returns the ascii difference of first odd characters of
compared strings .
public class StringCompareEmp{
public static void main(String args[]){
String str = "Hello World";
String anotherString = "hello world";
Object objStr = str;
System.out.println( str.compareTo(anotherString) );
System.out.println( str.compareToIgnoreCase(anotherString) );
System.out.println( str.compareTo(objStr.toString()));
}
}

Result:

Saikat Banerjee

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-32
0
0

How to search the last position of a substring ?

Solution:
This example shows how to determine the last position of a substring inside a string with the help of
strOrig.lastIndexOf(Stringname) method.
public class SearchlastString {
public static void main(String[] args) {
String strOrig = "Hello world ,Hello Reader";
int lastIndex = strOrig.lastIndexOf("Hello");
if(lastIndex == - 1){
System.out.println("Hello not found");
}else{
System.out.println("Last occurrence of Hello
is at index "+ lastIndex);
}
}
}

Result:
Last occurrence of Hello is at index 13

How to remove a particular character from a string ?

Solution:
Following example shows hoe to remove a character from a particular position from a string with the help of
removeCharAt(string,position) method.
public class Main {
public static void main(String args[]) {
String str = "this is Java";
System.out.println(removeCharAt(str, 3));
}
public static String removeCharAt(String s, int pos) {
return s.substring(0, pos) + s.substring(pos + 1);
}
}

Result:

Saikat Banerjee

Page 6

thi is Java

How to replace a substring inside a string by another one ?

Solution:
This example describes how replace method of java String class can be used to replace character or substring
by new one.
public class StringReplaceEmp{
String str="Hello World";
System.out.println( str.replace( 'H','W' ) );
System.out.println( str.replaceFirst("He", "Wa") );
System.out.println( str.replaceAll("He", "Ha") );
}
}

Result:
Wello World
Wallo World
Hallo World

How to reverse a String?

Solution:
Following example shows how to reverse a String after taking it from command line argument .The program
buffers the input String using StringBuffer(String string) method, reverse the buffer and then converts the
buffer into a String with the help of toString() method.
public class StringReverseExample{
public static void main(String[] args){
String string="abcdef";
String reverse = new StringBuffer(string).
reverse().toString();
System.out.println("nString before reverse:
"+string);
System.out.println("String after reverse:
"+reverse);
}
}

Result:

Saikat Banerjee

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String before reverse:abcdef
String after reverse:fedcba

How to search a word inside a string ?

Solution:
This example shows how we can search a word within a String object using indexOf() method which returns a
position index of a word within the string if found. Otherwise it returns -1.
public class SearchStringEmp{
String strOrig = "Hello readers";
int intIndex = strOrig.indexOf("Hello");
if(intIndex == - 1){
System.out.println("Hello not found");
}else{
System.out.println("Found Hello at index "
+ intIndex);
}
}
}

Result:
Found Hello at index 0

How to split a string into a number of substrings ?

Solution:
Following example splits a string into a number of substrings with the help of str split(string) method and then
prints the substrings.
public class JavaStringSplitEmp{
String str = "jan-feb-march";
String[] temp;
String delimeter = "-";
temp = str.split(delimeter);
for(int i =0; i < temp.length ; i++){
System.out.println(temp[i]);
System.out.println("");
str = "jan.feb.march";
delimeter = ".";
temp = str.split(delimeter);
}
for(int i =0; i < temp.length ; i++){

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temp = str.split(delimeter,2);
for(int j =0; j < temp.length ; j++){
}
}
}
}

Result:
jan
feb
march
jan
jan
jan
feb.march
feb.march
feb.march

How to convert a string totally into upper case?

Solution:
Following example changes the case of a string to upper case by using String toUpperCase() method.
public class StringToUpperCaseEmp {
String str = "string abc touppercase ";
String strUpper = str.toUpperCase();
System.out.println("Original String: " + str);
System.out.println("String changed to upper case: "
+ strUpper);
}
}

Result:
Original String: string abc touppercase
String changed to upper case: STRING ABC TOUPPERCASE

Saikat Banerjee

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How to match regions in strings ?

Solution:
Following example determines region matchs in two strings by using regionMatches() method.
public class StringRegionMatch{
String first_str = "Welcome to Microsoft";
String second_str = "I work with Microsoft";
boolean match = first_str.
regionMatches(11, second_str, 12, 9);
System.out.println("first_str[11 -19] == "
+ "second_str[12 - 21]:-"+ match);
}
}

Result:
first_str[11 -19] == second_str[12 - 21]:-true

How to compare performance of string creation ?

Solution:
Following example compares the performance of two strings created in two different ways.
public class StringComparePerformance{
long startTime = System.currentTimeMillis();
for(int i=0;i<50000;i++){
String s1 = "hello";
String s2 = "hello";
}
long endTime = System.currentTimeMillis();
System.out.println("Time taken for creation"
+ " of String literals : "+ (endTime - startTime)
+ " milli seconds" );
long startTime1 = System.currentTimeMillis();
for(int i=0;i<50000;i++){
String s3 = new String("hello");
String s4 = new String("hello");
}
long endTime1 = System.currentTimeMillis();
System.out.println("Time taken for creation"
+ " of String objects : " + (endTime1 - startTime1)
+ " milli seconds");
}
}

Saikat Banerjee

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Result:
The above code sample will produce the following result.The result may vary.
Time taken for creation of String literals : 0 milli seconds
Time taken for creation of String objects : 16 milli seconds

How to optimize string creation ?

Solution:
Following example optimizes string creation by using String.intern() method.
public class StringOptimization{
String variables[] = new String[50000];
for( int i=0;i <50000;i++){
variables[i] = "s"+i;
}
for(int i=0;i<50000;i++){
variables[i] = "hello";
}
System.out.println("Creation time"
+ " of String literals : "+ (endTime0 - startTime0)
+ " ms" );
for(int i=0;i<50000;i++){
variables[i] = new String("hello");
}
System.out.println("Creation time of"
+ " String objects with 'new' key word : "
+ (endTime1 - startTime1)
+ " ms");
for(int i=0;i<50000;i++){
variables[i] = new String("hello");
variables[i] = variables[i].intern();
}
System.out.println("Creation time of"
+ " String objects with intern(): "
+ (endTime2 - startTime2)
+ " ms");
}
}

Result:
Creation time of String literals : 0 ms
Creation time of String objects with 'new' key word : 31 ms

Saikat Banerjee

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Creation time of String objects with intern(): 16 ms

How to format strings ?

Solution:
Following example returns a formatted string value by using a specific locale, format and arguments in format()
method
import java.util.*;
public class StringFormat{
double e = Math.E;
System.out.format("%f%n", e);
System.out.format(Locale.GERMANY, "%-10.4f%n%n", e);
}
}

Result:
2.718282
2,7183

How to optimize string concatenation ?

Solution:
Following example shows performance of concatenation by using "+" operator and StringBuffer.append()
method.
public class StringConcatenate{
long startTime = System.currentTimeMillis();
for(int i=0;i<5000;i++){
String result = "This is"
+ "testing the"
+ "difference"+ "between"
+ "String"+ "and"+ "StringBuffer";
}
long endTime = System.currentTimeMillis();
System.out.println("Time taken for string"
+ "concatenation using + operator : "
+ (endTime - startTime)+ " ms");
for(int i=0;i<5000;i++){
StringBuffer result = new StringBuffer();
result.append("This is");
result.append("testing the");

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result.append("difference");
result.append("between");
result.append("String");
result.append("and");
result.append("StringBuffer");
}
System.out.println("Time taken for String concatenation"
+ "using StringBuffer : "
+ (endTime1 - startTime1)+ " ms");
}
}

Result:
Time taken for stringconcatenation using + operator : 0 ms
Time taken for String concatenationusing StringBuffer : 16 ms

How to determine the Unicode code point in string ?

Solution:
This example shows you how to use codePointBefore() method to return the character (Unicode code point)
before the specified index.
public class StringUniCode{
String test_string="Welcome to Sbdsi.saikat";
System.out.println("String under test is = "+test_string);
System.out.println("Unicode code point at"
+" position 5 in the string is = "
+ test_string.codePointBefore(5));
}
}

Result:
String under test is = Welcome to Sbdsi.saikat
Unicode code point at position 5 in the string is =111

How to buffer strings ?

Solution:
Following example buffers strings and flushes it by using emit() method.

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public class StringBuffer{
countTo_N_Improved();
}
private final static int MAX_LENGTH=30;
private static String buffer = "";
private static void emit(String nextChunk) {
if(buffer.length() + nextChunk.length() > MAX_LENGTH) {
System.out.println(buffer);
buffer = "";
}
buffer += nextChunk;
}
private static final int N=100;
private static void countTo_N_Improved() {
for (int count=2; count<=N; count=count+2) {
emit(" " + count);
}
}
}

Result:
2 4 6
24 26
44 46
64 66

8 10 12 14 16 18 20 22
28 30 32 34 36 38 40 42
48 50 52 54 56 58 60 62
68 70 72 74 76 78 80 82

Java Arrays - Programming Examples
Learn how to play with arrays in Java programming. Here are most commonly used examples:
1. How to sort an array and search an element inside it?
2. How to sort an array and insert an element inside it?
3. How to determine the upper bound of a two dimentional array?
4. How to reverse an array?
5. How to write an array of strings to the output console?
6. How to search the minimum and the maximum element in an array?
7. How to merge two arrays?
8. How to fill (initialize at once) an array?
9. How to extend an array after initialisation?
10. How to sort an array and search an element inside it?
11. How to remove an element of array?
12. How to remove one array from another array?
13. How to find common elements from arrays?
14. How to find an object or a string in an Array?
15. How to check if two arrays are equal or not?
16. How to compare two arrays?

How to sort an array and search an element inside it?

Saikat Banerjee

Page 14

Solution:
Following example shows how to use sort () and binarySearch () method to accomplish the task. The user
defined method printArray () is used to display the output:
import java.util.Arrays;
public class MainClass {
public static void main(String args[]) throws Exception {
int array[] = { 2, 5, -2, 6, -3, 8, 0, -7, -9, 4 };
Arrays.sort(array);
printArray("Sorted array", array);
int index = Arrays.binarySearch(array, 2);
System.out.println("Found 2 @ " + index);
}
private static void printArray(String message, int array[]) {
System.out.println(message
+ ": [length: " + array.length + "]");
for (int i = 0; i < array.length; i++) {
if(i != 0){
System.out.print(", ");
}
System.out.print(array[i]);
}
System.out.println();
}
}

Result:
Sorted array: [length: 10]
-9, -7, -3, -2, 0, 2, 4, 5, 6, 8
Found 2 @ 5

How to sort an array and insert an element inside it?

Solution:
Following example shows how to use sort () method and user defined method insertElement ()to accomplish
the task.
int array[] = { 2, 5, -2, 6, -3, 8, 0, -7, -9, 4 };
Arrays.sort(array);
System.out.println("Didn't find 1 @ "
+ index);
int newIndex = -index - 1;
array = insertElement(array, 1, newIndex);

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printArray("With 1 added", array);
}
if (i != 0){
}
}
}
private static int[] insertElement(int original[],
int element, int index) {
int length = original.length;
int destination[] = new int[length + 1];
System.arraycopy(original, 0, destination, 0, index);
destination[index] = element;
System.arraycopy(original, index, destination, index
+ 1, length - index);
return destination;
}
}

Result:
-9, -7, -3, -2, 0, 2, 4, 5, 6, 8
Didn't find 1 @ -6
With 1 added: [length: 11]
-9, -7, -3, -2, 0, 1, 2, 4, 5, 6, 8

How to determine the upper bound of a two dimentional array ?

Solution:
Following example helps to determine the upper bound of a two dimentional array with the use of
arrayname.length.
public class Main {
String[][] data = new String[2][5];
System.out.println("Dimension 1: " + data.length);
System.out.println("Dimension 2: " + data[0].length);
}
}

Result:

Saikat Banerjee

Page 16

Dimension 1: 2
Dimension 2: 5

How to reverse an array list ?

Solution:
Following example reverses an array list by using Collections.reverse(ArrayList)method.
import java.util.ArrayList;
import java.util.Collections;
public class Main {
ArrayList arrayList = new ArrayList();
arrayList.add("A");
arrayList.add("B");
arrayList.add("C");
arrayList.add("D");
arrayList.add("E");
System.out.println("Before Reverse Order: " + arrayList);
Collections.reverse(arrayList);
System.out.println("After Reverse Order: " + arrayList);
}
}

Result:
Before Reverse Order: [A, B, C, D, E]
After Reverse Order: [E, D, C, B, A]

How to write an array of strings to the output console ?

Solution:
Following example demonstrates writing elements of an array to the output console through looping.
public class Welcome {
String[] greeting = new String[3];
greeting[0] = "This is the greeting";
greeting[1] = "for all the readers from";
greeting[2] = "Java Source .";
for (int i = 0; i < greeting.length; i++){
System.out.println(greeting[i]);
}
}
}

Saikat Banerjee

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Result:
This is the greeting
For all the readers From
Java source .

How to search the minimum and the maximum element in an array ?

Solution:
This example shows how to search the minimum and maximum element in an array by using Collection.max()
and Collection.min() methods of Collection class .
public class Main {
Integer[] numbers = { 8, 2, 7, 1, 4, 9, 5};
int min = (int) Collections.min(Arrays.asList(numbers));
int max = (int) Collections.max(Arrays.asList(numbers));
System.out.println("Min number: " + min);
System.out.println("Max number: " + max);
}
}

Result:
Min number: 1
Max number: 9

How to merge two arrays ?

Solution:
This example shows how to merge two arrays into a single array by the use of list.Addall(array1.asList(array2)
method of List class and Arrays.toString () method of Array class.
import java.util.List;
public class Main {
String a[] = { "A", "E", "I" };

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String b[] = { "O", "U" };
List list = new ArrayList(Arrays.asList(a));
list.addAll(Arrays.asList(b));
Object[] c = list.toArray();
System.out.println(Arrays.toString(c));
}
}

Result:
[A, E, I, O, U]

How to fill (initialize at once) an array ?

Solution:
This example fill (initialize all the elements of the array in one short) an array by using
Array.fill(arrayname,value) method and Array.fill(arrayname ,starting index ,ending index ,value) method of
Java Util class.
import java.util.*;
public class FillTest {
int array[] = new int[6];
Arrays.fill(array, 100);
for (int i=0, n=array.length; i < n; i++) {
System.out.println(array[i]);
}
Arrays.fill(array, 3, 6, 50);
for (int i=0, n=array.length; i< n; i++) {
System.out.println(array[i]);
}
}
}

Result:
100
100
100
100
100
100
100
100
100
50

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50
50

How to extend an array after initialisation?

Solution:
Following example shows how to extend an array after initialization by creating an new array.
public class Main {
String[] names = new String[] { "A", "B", "C" };
String[] extended = new String[5];
extended[3] = "D";
extended[4] = "E";
System.arraycopy(names, 0, extended, 0, names.length);
for (String str : extended){
System.out.println(str);
}
}
}

Result:
A
B
C
D
E

How to sort an array and search an element inside it?

Solution:
Following example shows how to use sort () and binarySearch () method to accomplish the task. The user
defined method printArray () is used to display the output:
int array[] = { 2, 5, -2, 6, -3, 8, 0, -7, -9, 4 };
Arrays.sort(array);
System.out.println("Found 2 @ " + index);
}

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if(i != 0){
}
}
}
}

Result:
-9, -7, -3, -2, 0, 2, 4, 5, 6, 8
Found 2 @ 5

How to remove an element of array?

Solution:
Following example shows how to remove an element from array.
public class Main {
ArrayList objArray = new ArrayList();
objArray.clear();
objArray.add(0,"0th element");
objArray.add(1,"1st element");
objArray.add(2,"2nd element");
System.out.println("Array before removing an
element"+objArray);
objArray.remove(1);
objArray.remove("0th element");
System.out.println("Array after removing an
element"+objArray);
}
}

Result:
Array before removing an element[0th element,
1st element, 2nd element]
Array after removing an element[0th element]

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How to remove one array from another array?

Solution:
Following example uses Removeall method to remove one array from another.
public class Main {
ArrayList objArray2 = new ArrayList();
objArray2.add(0,"common1");
objArray2.add(2,"notcommon");
objArray2.add(3,"notcommon1");
objArray.add(0,"common1");
objArray.add(2,"notcommon2");
System.out.println("Array elements of array1" +objArray);
System.out.println("Array elements of array2" +objArray2);
objArray.removeAll(objArray2);
System.out.println("Array1 after removing
array2 from array1"+objArray);
}
}

Result:
Array elements of array1[common1, common2, notcommon2]
Array elements of array2[common1, common2, notcommon,
notcommon1]
Array1 after removing array2 from array1[notcommon2]

How to find common elements from arrays?

Solution:
Following example shows how to find common elements from two arrays and store them in an array.
public class Main {

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objArray.add(2,"notcommon2");
System.out.println("Array elements of array1"+objArray);
System.out.println("Array elements of array2"+objArray2);
objArray.retainAll(objArray2);
System.out.println("Array1 after retaining common
elements of array2 & array1"+objArray);
}
}

Result:
Array elements of array1[common1, common2, notcommon2]
Array elements of array2[common1, common2, notcommon,
notcommon1]
Array1 after retaining common elements of array2 & array1
[common1, common2]

How to find an object or a string in an Array?

Solution:
Following example uses Contains method to search a String in the Array.
public class Main {
System.out.println("Array elements of array1"+objArray);
System.out.println("Array elements of array2"+objArray2);
System.out.println("Array 1 contains String common2?? "
+objArray.contains("common1"));
System.out.println("Array 2 contains Array1?? "
+objArray2.contains(objArray) );
}
}

Result:
Array elements of array1[common1, common2]
Array elements of array2[common1, common2, notcommon, notcommon1]

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Array 1 contains String common2?? true
Array 2 contains Array1?? false

How to check if two arrays are equal or not?

Solution:
Following example shows how to use equals () method of Arrays to check if two arrays are equal or not.
public class Main {
public static void main(String[] args) throws Exception {
int[] ary = {1,2,3,4,5,6};
int[] ary1 = {1,2,3,4,5,6};
int[] ary2 = {1,2,3,4};
System.out.println("Is array 1 equal to array 2?? "
+Arrays.equals(ary, ary1));
}
}

Result:
Is array 1 equal to array 2?? true
Is array 1 equal to array 3?? false

How to compare two arrays?

Solution:
Following example uses equals method to check whether two arrays are or not.
public class Main {
int[] ary = {1,2,3,4,5,6};
int[] ary1 = {1,2,3,4,5,6};
int[] ary2 = {1,2,3,4};
}
}

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Result:
Is array 1 equal to array 2?? true
Is array 1 equal to array 3?? false

Java Date & Time - Programming Examples
Learn how to play with data and time in Java programming. Here are most commonly used examples:
1. How to format time in AM-PM format?
2. How to display name of a month in (MMM) format ?
3. How to display hour and minute?
4. How to display current date and time?
5. How to format time in 24 hour format?
6. How to format time in MMMM format?
7. How to format seconds?
8. How to display name of the months in short format?
9. How to display name of the weekdays?
10. How to add time to Date?
11. How to display time in different country's format?
12. How to display time in different languages?
13. How to roll through hours & months?
14. How to find which week of the year?
15. How to display date in different formats ?

How to format time in AM-PM format?

Solution:
This example formats the time by using SimpleDateFormat("HH-mm-ss a") constructor and sdf.format(date)
method of SimpleDateFormat class.
import java.text.SimpleDateFormat;
import java.util.Date;
public class Main{
Date date = new Date();
String strDateFormat = "HH:mm:ss a";
SimpleDateFormat sdf = new SimpleDateFormat(strDateFormat);
System.out.println(sdf.format(date));
}
}

Result:
The above code sample will produce the following result.The result will change depending upon the current
system time

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Page 25

06:40:32 AM

How to display name of a month in (MMM) format ?

Solution:
This example shows how to display the current month in the (MMM) format with the help of
Calender.getInstance() method of Calender class and fmt.format() method of Formatter class.
import java.util.Calendar;
import java.util.Formatter;
public class MainClass{
Formatter fmt = new Formatter();
Calendar cal = Calendar.getInstance();
fmt = new Formatter();
fmt.format("%tB %tb %tm", cal, cal, cal);
System.out.println(fmt);
}
}

Result:
October Oct 10

How to display hour and minute ?

Solution:
This example demonstrates how to display the hour and minute of that moment by using Calender.getInstance()
of Calender class.
fmt.format("%tl:%tM", cal, cal);
}
}

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Result:
The above code sample will produce the following result.The result will chenge depending upon the current
system time.
03:20

How to display current date and time?

Solution:
This example shows how to display the current date and time using Calender.getInstance() method of Calender
class and fmt.format() method of Formatter class.
fmt.format("%tc", cal);
}
}

Result:
system date and time
Wed Oct 15 20:37:30 GMT+05:30 2008

How to format time in 24 hour format?

Solution:
This example formats the time into 24 hour format (00:00-24:00) by using sdf.format(date) method of
SimpleDateFormat class.
public class Main {
SimpleDateFormat sdf = new SimpleDateFormat("h");
System.out.println("hour in h format : "

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+ sdf.format(date));
}
}

Result:
hour in h format : 8

How to format time in MMMM format?

Solution:
This example formats the month with the help of SimpleDateFormat(�MMMM�) constructor and
sdf.format(date) method of SimpleDateFormat class.
public class Main{
SimpleDateFormat sdf = new SimpleDateFormat("MMMM");
System.out.println("Current Month in MMMM format : "
}
}

Result:
system date
Current Month in MMMM format : May

How to format seconds?

Solution:
This example formats the second by using SimpleDateFormat(�ss�) constructor and sdf.format(date) method
of SimpleDateFormat class.
public class Main{

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SimpleDateFormat sdf = new SimpleDateFormat("ss");
System.out.println("seconds in ss format : "
}
}

Result:
system time.
seconds in ss format : 14

How to display name of the months in short format?

Solution:
This example displays the names of the months in short form with the help of
DateFormatSymbols().getShortMonths() method of DateFormatSymbols class.
import java.text.DateFormatSymbols;
public class Main {
String[] shortMonths = new DateFormatSymbols()
.getShortMonths();
for (int i = 0; i < (shortMonths.length-1); i++) {
String shortMonth = shortMonths[i];
System.out.println("shortMonth = " + shortMonth);
}
}
}

Result:
shortMonth
shortMonth
shortMonth
shortMonth
shortMonth
shortMonth
shortMonth
shortMonth
shortMonth
shortMonth
shortMonth
shortMonth

=
=
=
=
=
=
=
=
=
=
=
=

Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

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Page 29

How to display name of the weekdays ?

Solution:
This example displays the names of the weekdays in short form with the help of
DateFormatSymbols().getWeekdays() method of DateFormatSymbols class.
import java.text.DateFormatSymbols;
public class Main {
String[] weekdays = new DateFormatSymbols().getWeekdays();
for (int i = 2; i < (weekdays.length-1); i++) {
String weekday = weekdays[i];
System.out.println("weekday = " + weekday);
}
}
}

Result:
weekday
weekday
weekday
weekday
weekday

=
=
=
=
=

Monday
Tuesday
Wednesday
Thursday
Friday

How to add time(Days, years , seconds) to Date?

Solution:
The following examples shows us how to add time to a date using add() method of Calender.
import java.util.*;
public class Main {
Date d1 = new Date();
Calendar cl = Calendar. getInstance();
cl.setTime(d1);
System.out.println("today is " + d1.toString());
cl. add(Calendar.MONTH, 1);
System.out.println("date after a month will be "
+ cl.getTime().toString() );
cl. add(Calendar.HOUR, 70);
System.out.println("date after 7 hrs will be "
cl. add(Calendar.YEAR, 3);
System.out.println("date after 3 years will be "

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}
}

Result:
today is Mon
date after a
date after 7
date after 3

Jun 22 02:47:02 IST 2009
month will be Wed Jul 22 02:47:02 IST 2009
hrs will be Wed Jul 22 09:47:02 IST 2009
years will be Sun Jul 22 09:47:02 IST 2012

How to display time in different country's format?

Solution:
Following example uses Locale class & DateFormat class to disply date in different Country's format.
import java.text.DateFormat;
import java.util.*;
public class Main {
System.out.println("today is "+ d1.toString());
Locale locItalian = new Locale("it","ch");
DateFormat df = DateFormat.getDateInstance
(DateFormat.FULL, locItalian);
System.out.println("today is in Italian Language
in Switzerland Format : "+ df.format(d1));
}
}

Result:
today is Mon Jun 22 02:37:06 IST 2009
today is in Italian Language in Switzerlandluned�,
22. giugno 2009

How to display time in different languages?

Solution:
This example uses DateFormat class to display time in Italian.

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import java.text.DateFormat;
import java.util.*;
public class Main {
Locale locItalian = new Locale("it");
DateFormat df = DateFormat.getDateInstance
(DateFormat.FULL, locItalian);
System.out.println("today is "+ df.format(d1));
}
}

Result:
today is luned� 22 giugno 2009

How to roll through hours & months?

Solution:
This example shows us how to roll through monrhs (without changing year) or hrs(without changing month or
year) using roll() method of Class calender.
import java.util.*;
public class Main {
cl.setTime(d1);
cl. roll(Calendar.MONTH, 100);
System.out.println("date after a month will be "
cl. roll(Calendar.HOUR, 70);
System.out.println("date after 7 hrs will be "
}
}

Result:
date after a month will be Thu Oct 22 02:44:36 IST 2009
date after 7 hrs will be Thu Oct 22 00:44:36 IST 2009

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How to find which week of the year, month?

Solution:
The following example displays week no of the year & month.
import java.util.*;
public class Main {
cl.setTime(d1);
System.out.println("today is "
+ cl.WEEK_OF_YEAR+ " week of the year");
System.out.println("today is a "+cl.DAY_OF_MONTH +
"month of the year");
System.out.println("today is a "+cl.WEEK_OF_MONTH
+"week of the month");
}
}

Result:
today is 30 week of the year
today is a 5month of the year
today is a 4week of the month

How to display date in different formats ?

Solution:
This example displays the names of the weekdays in short form with the help of
DateFormatSymbols().getWeekdays() method of DateFormatSymbols class.
import java.text.*;
import java.util.*;
public class Main {
Date dt = new Date(1000000000000L);
DateFormat[] dtformat = new DateFormat[6];
dtformat[0] = DateFormat.getInstance();
dtformat[1] = DateFormat.getDateInstance();
dtformat[2] = DateFormat.getDateInstance(DateFormat.MEDIUM);
dtformat[3] = DateFormat.getDateInstance(DateFormat.FULL);
dtformat[4] = DateFormat.getDateInstance(DateFormat.LONG);
dtformat[5] = DateFormat.getDateInstance(DateFormat.SHORT);
for(DateFormat dateform : dtformat)

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System.out.println(dateform.format(dt));
}
}

Result:
9/9/01 7:16 AM
Sep 9, 2001
Sep 9, 2001
Sunday, September 9, 2001
September 9, 2001
9/9/01

Java Method - Programming Examples
Learn how to play with methods in Java programming. Here are most commonly used examples:
1. How to overload methods?
2. How to use method overloading for printing different types of array?
3. How to use method for solving Tower of Hanoi problem?
4. How to use method for calculating Fibonacci series?
5. How to use method for calculating Factorial of a number?
6. How to use method overriding in Inheritance for subclasses?
7. How to display Object class using instanceOf keyword?
8. How to use break to jump out of a loop in a method?
9. How to use continue in a method?
10. How to use Label in a method?
11. How to use enum & switch statement ?
12. How to make enum constructor, instance variable & method?
13. How to use for and foreach loop for printing values of an array ?
14. How to make a method take variable lentgth argument as an input?
15. How to use variable arguments as an input when dealing with method overloading?

How to overload methods ?

Solution:
This example displays the way of overloading a method depending on type and number of parameters.
class MyClass {
int height;
MyClass() {
System.out.println("bricks");
height = 0;
}
MyClass(int i) {
System.out.println("Building new House that is "
+ i + " feet tall");
height = i;

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}
void info() {
System.out.println("House is " + height
+ " feet tall");
}
void info(String s) {
System.out.println(s + ": House is "
+ height + " feet tall");
}
}
MyClass t = new MyClass(0);
t.info();
t.info("overloaded method");
//Overloaded constructor:
new MyClass();
}
}

Result:
Building new House that is 0 feet tall.
House is 0 feet tall.
Overloaded method: House is 0 feet tall.
bricks

How to use method overloading for printing different types of array ?

Solution:
This example displays the way of using overloaded method for printing types of array (integer, double and
character).
public static void printArray(Integer[] inputArray) {
for (Integer element : inputArray){
System.out.printf("%s ", element);
}
}
public static void printArray(Double[] inputArray) {
for (Double element : inputArray){
}
}
public static void printArray(Character[] inputArray) {
for (Character element : inputArray){
}
}

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Page 35

Integer[] integerArray = { 1, 2, 3, 4, 5, 6 };
Double[] doubleArray = { 1.1, 2.2, 3.3, 4.4,
5.5, 6.6, 7.7 };
Character[] characterArray = { 'H', 'E', 'L', 'L', 'O' };
System.out.println("Array integerArray contains:");
printArray(integerArray);
System.out.println("nArray doubleArray contains:");
printArray(doubleArray);
System.out.println("nArray characterArray contains:");
printArray(characterArray);
}
}

Result:
Array integerArray contains:
1
2
3
4
5
6
Array doubleArray contains:
1.1
2.2
3.3
4.4
5.5
6.6
7.7
Array characterArray contains:
H
E
L
L
O

How to use method for solving Tower of Hanoi problem?

Solution:
This example displays the way of using method for solving Tower of Hanoi problem( for 3 disks).
int nDisks = 3;
doTowers(nDisks, 'A', 'B', 'C');
}
public static void doTowers(int topN, char from,
char inter, char to) {
if (topN == 1){
System.out.println("Disk 1 from "
+ from + " to " + to);

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Page 36

}else {
doTowers(topN - 1, from, to, inter);
System.out.println("Disk "
+ topN + " from " + from + " to " + to);
doTowers(topN - 1, inter, from, to);
}
}
}

Result:
Disk
Disk
Disk
Disk
Disk
Disk
Disk

1
2
1
3
1
2
1

from
from
from
from
from
from
from

A
A
C
A
B
B
A

to
to
to
to
to
to
to

C
B
B
C
A
C
C

How to use method for calculating Fibonacci series?

Solution:
This example shows the way of using method for calculating Fibonacci Series upto n numbers.
public static long fibonacci(long number) {
if ((number == 0) || (number == 1))
return number;
else
return fibonacci(number - 1) + fibonacci(number - 2);
}
for (int counter = 0; counter <= 10; counter++){
System.out.printf("Fibonacci of %d is: %dn",
counter, fibonacci(counter));
}
}
}

Result:
Fibonacci
Fibonacci
Fibonacci
Fibonacci
Fibonacci
Fibonacci
Fibonacci
Fibonacci

of
of
of
of
of
of
of
of

0
1
2
3
4
5
6
7

is:
is:
is:
is:
is:
is:
is:
is:

Saikat Banerjee

0
1
1
2
3
5
8
13

Page 37

Fibonacci of 8 is: 21

How to use method for calculating Factorial of a number?

Solution:
This example shows the way of using method for calculating Factorial of 9(nine) numbers.
for (int counter = 0; counter <= 10; counter++){
System.out.printf("%d! = %dn", counter,
factorial(counter));
}
}
public static long factorial(long number) {
if (number <= 1)
return 1;
else
return number * factorial(number - 1);
}
}

Result:
0! = 1
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
7! = 5040
8! = 40320
9! = 362880
10! = 3628800

How to use method overriding in Inheritance for subclasses ?

Solution:
This example demonstrates the way of method overriding by subclasses with different number and type of
parameters.
public class Findareas{
public static void main (String []agrs){
Figure f= new Figure(10 , 10);

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Rectangle r= new Rectangle(9 , 5);
Figure figref;
figref=f;
System.out.println("Area is :"+figref.area());
figref=r;
System.out.println("Area is :"+figref.area());
}
}
class Figure{
double dim1;
double dim2;
Figure(double a , double b) {
dim1=a;
dim2=b;
}
Double area() {
System.out.println("Inside area for figure.");
return(dim1*dim2);
}
}
class Rectangle extends Figure {
Rectangle(double a, double b) {
super(a ,b);
}
Double area() {
System.out.println("Inside area for rectangle.");
return(dim1*dim2);
}
}

Result:
Inside area for figure.
Area is :100.0
Inside area for rectangle.
Area is :45.0

How to display Object class using instanceOf keyword?

Solution:
This example makes displayObjectClass() method to display the Class of the Object that is passed in this
method as an argument.
import java.util.Vector;
public class Main {
Object testObject = new ArrayList();
displayObjectClass(testObject);
}
public static void displayObjectClass(Object o) {

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Page 39

if (o instanceof Vector)
System.out.println("Object was an instance
of the class java.util.Vector");
else if (o instanceof ArrayList)
System.out.println("Object was an instance of
the class java.util.ArrayList");
else
System.out.println("Object was an instance of the "
+ o.getClass());
}
}

Result:
Object was an instance of the class java.util.ArrayList

How to use break to jump out of a loop in a method?

Solution:
This example uses the 'break' to jump out of the loop.
public class Main {
int[] intary = { 99,12,22,34,45,67,5678,8990 };
int no = 5678;
int i = 0;
boolean found = false;
for ( ; i < intary.length; i++) {
if (intary[i] == no) {
found = true;
break;
}
}
if (found) {
System.out.println("Found the no: " + no
+ " at index: " + i);
}
else {
System.out.println(no + "not found in the array");
}
}
}

Result:
Found the no: 5678 at

index: 6

Java Files - Programming Examples
Saikat Banerjee

Page 40

Learn how to play with Files in Java programming. Here are most commonly used examples:
1. How to compare paths of two files?
2. How to create a new file?
3. How to get last modification date of a file?
4. How to create a file in a specified directory?
5. How to check a file exist or not?
6. How to make a file read-only?
7. How to renaming a file ?
8. How to get a file's size in bytes?
9. How to change the last modification time of a file ?
10. How to create a temporary file?
11. How to append a string in an existing file?
12. How to copy one file into another file?
13. How to delete a file?
14. How to read a file?
15. How to write to a file?

How to compare paths of two files ?

Solution:
This example shows how to compare paths of two files in a same directory by the use of
filename.compareTo(another filename) method of File class.
import java.io.File;
public class Main {
File file1 = new File("C:/File/demo1.txt");
File file2 = new File("C:/java/demo1.txt");
if(file1.compareTo(file2) == 0) {
System.out.println("Both paths are same!");
} else {
System.out.println("Paths are not same!");
}
}
}

Result:
Paths are not same!

How to create a new file?

Saikat Banerjee

Page 41

Solution:
This example demonstrates the way of creating a new file by using File() constructor and file.createNewFile()
method of File class.
import java.io.IOException;
public class Main {
try{
File file = new File("C:/myfile.txt");
if(file.createNewFile())
System.out.println("Success!");
else
System.out.println
("Error, file already exists.");
}
catch(IOException ioe) {
ioe.printStackTrace();
}
}
}

Result:
The above code sample will produce the following result (if "myfile.txt does not exist before)
Success!

How to get last modification date of a file ?

Solution:
This example shows how to get the last modification date of a file using file.lastModified() method of File
class.
public class Main {
File file = new File("Main.java");
Long lastModified = file.lastModified();
Date date = new Date(lastModified);
System.out.println(date);
}
}

Result:

Saikat Banerjee

Page 42

Tue 12 May 10:18:50 PDF 2009

How to create a file in a specified directory ?

Solution:
This example demonstrates how to create a file in a specified directory using File.createTempFile() method of
File class.
public class Main {
public static void main(String[] args)
throws Exception {
File file = null;
File dir = new File("C:/");
file = File.createTempFile
("JavaTemp", ".javatemp", dir);
System.out.println(file.getPath());
}
}

Result:
C:JavaTemp37056.javatemp

How to check a file exist or not?

Solution:
This example shows how to check a file�s existence by using file.exists() method of File class.
public class Main {
File file = new File("C:/java.txt");
System.out.println(file.exists());
}
}

Result:
The above code sample will produce the following result (if the file "java.txt" exists in 'C' drive).
true

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Page 43

How to make a file read-only?

Solution:
This example demonstrates how to make a file read-only by using file.setReadOnly() and file.canWrite()
methods of File class .
public class Main {
File file = new File("C:/java.txt");
System.out.println(file.setReadOnly());
System.out.println(file.canWrite());
}
}

Result:
The above code sample will produce the following result.To test the example,first create a file 'java.txt' in 'C'
drive.
true
false

How to rename a file?

Solution:
This example demonstrates how to renaming a file using oldName.renameTo(newName) method of File class.
public class Main {
File oldName = new File("C:/program.txt");
File newName = new File("C:/java.txt");
if(oldName.renameTo(newName)) {
System.out.println("renamed");
} else {
System.out.println("Error");
}
}
}

Result:
The above code sample will produce the following result.To test this example, first create a file 'program.txt' in
'C' drive.

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Page 44

renamed

How to get a file�s size in bytes ?

Solution:
This example shows how to get a file's size in bytes by using file.exists() and file.length() method of File class.
public class Main {
public static long getFileSize(String filename) {
File file = new File(filename);
if (!file.exists() || !file.isFile()) {
System.out.println("File doesn't exist");
return -1;
}
return file.length();
}
long size = getFileSize("c:/java.txt");
System.out.println("Filesize in bytes: " + size);
}
}

Result:
The above code sample will produce the following result.To test this example, first create a text file 'java.txt' in
'C' drive.The size may vary depending upon the size of the file.
File size in bytes: 480

How to change the last modification time of a file ?

Solution:
This example shows how to change the last modification time of a file with the help of
fileToChange.lastModified() and fileToChange setLastModified() methods of File class .
public class Main {
throws Exception {
File fileToChange = new File
("C:/myjavafile.txt");
fileToChange.createNewFile();
Date filetime = new Date
(fileToChange.lastModified());

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System.out.println(filetime.toString());
System.out.println
(fileToChange.setLastModified
(System.currentTimeMillis()));
filetime = new Date
(fileToChange.lastModified());
System.out.println(filetime.toString());
}
}

Result:
The above code sample will produce the following result.The result may vary depending upon the system time.
Sat Oct 18 19:58:20 GMT+05:30 2008
true
Sat Oct 18 19:58:20 GMT+05:30 2008

How to create a temporary file?

Solution:
This example shows how to create a temporary file using createTempFile() method of File class.
import java.io.*;
public class Main {
throws Exception {
File temp = File.createTempFile
("pattern", ".suffix");
temp.deleteOnExit();
BufferedWriter out = new BufferedWriter
(new FileWriter(temp));
out.write("aString");
System.out.println("temporary file created:");
out.close();
}
}

Result:
temporary file created:

How to append a string in an existing file?

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Page 46

Solution:
This example shows how to append a string in an existing file using filewriter method.
import java.io.*;
public class Main {
try {
(new FileWriter("filename"));
out.write("aString1n");
out.close();
out = new BufferedWriter(new FileWriter
("filename",true));
out.write("aString2");
out.close();
BufferedReader in = new BufferedReader
(new FileReader("filename"));
String str;
while ((str = in.readLine()) != null) {
}
}
in.close();
catch (IOException e) {
System.out.println("exception occoured"+ e);
}
}
}

Result:
aString1
aString2

How to copy one file into another file?

Solution:
This example shows how to copy contents of one file into another file using read & write methods of
BufferedWriter class.
import java.io.*;
public class Main {
throws Exception {
BufferedWriter out1 = new BufferedWriter
(new FileWriter("srcfile"));
out1.write("string to be copiedn");
out1.close();
InputStream in = new FileInputStream

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Page 47

(new File("srcfile"));
OutputStream out = new FileOutputStream
(new File("destnfile"));
byte[] buf = new byte[1024];
int len;
while ((len = in.read(buf)) > 0) {
out.write(buf, 0, len);
}
in.close();
out.close();
BufferedReader in1 = new BufferedReader
(new FileReader("destnfile"));
String str;
while ((str = in1.readLine()) != null) {
}
in.close();
}
}

Result:
string to be copied

How to delete a file?

Solution:
This example shows how to delete a file using delete() method of File class.
import java.io.*;
public class Main {
try {
(new FileWriter("filename"));
out.write("aString1n");
out.close();
boolean success = (new File
("filename")).delete();
if (success) {
System.out.println("The file has
been successfully deleted");
}
(new FileReader("filename"));
String str;
}
in.close();
}
System.out.println("exception occoured"+ e);

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System.out.println("File does not exist
or you are trying to read a file that
has been deleted");
}
}
}
}

Result:
The file has been successfully deleted
exception occouredjava.io.FileNotFoundException:
filename (The system cannot find the file specified)
File does not exist or you are trying to read a
file that has been deleted

How to read a file?

Solution:
This example shows how to read a file using readLine method of BufferedReader class.
import java.io.*;
public class Main {
try {
(new FileReader("c:filename"));
String str;
}
}
}
}
}
}

Result:
aString

How to write into a file ?

Saikat Banerjee

Page 49

Solution:
This example shows how to write to a file using write method of BufferedWriter.
import java.io.*;
public class Main {
try {
BufferedWriter out = new
BufferedWriter(new FileWriter("outfilename"));
out.write("aString");
out.close();
System.out.println
("File created successfully");
}
}
}
}

Result:
File created successfully.

Java Directory - Programming Examples
Learn how to accsess directories in Java programming. Here are most commonly used examples:
1. How to create directories recursively?
2. How to delete a directory?
3. How to get the fact that a directory is empty or not?
4. How to get a directory is hidden or not?
5. How to print the directory hierarchy?
6. How to print the last modification time of a directory?
7. How to get the parent directory of a file?
8. How to search all files inside a directory?
9. How to get the size of a directory?
10. How to traverse a directory?
11. How to find current working directory?
12. How to display root directories in the system?
13. How to search for a file in a directory?
14. How to display all the files in a directory?
15. How to display all the directories in a directory?

How to create directories recursively ?

Saikat Banerjee

Page 50

Solution:
Following example shows how to create directories recursively with the help of file.mkdirs() methods of File
class.
public class Main {
String directories = "D:abcdefghi";
File file = new File(directories);
boolean result = file.mkdirs();
System.out.println("Status = " + result);
}
}

Result:
Status = true

How to delete a directory?

Solution:
Following example demonstares how to delete a directory after deleting its files and directories by the use
ofdir.isDirectory(),dir.list() and deleteDir() methods of File class.
public class Main {
public static void main(String[] argv) throws Exception {
deleteDir(new File("c:temp"));
}
public static boolean deleteDir(File dir) {
if (dir.isDirectory()) {
String[] children = dir.list();
for (int i = 0; i < children.length; i++) {
boolean success = deleteDir
(new File(dir, children[i]));
if (!success) {
return false;
}
}
}
return dir.delete();
System.out.println("The directory is deleted.");
}
}

Result:

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Page 51

The directory is deleted.

How to get the fact that a directory is empty or not?

Solution:
Following example gets the size of a directory by using file.isDirectory(),file.list() and file.getPath() methodsof
File class.
public class Main {
File file = new File("/data");
if (file.isDirectory()) {
String[] files = file.list();
if (files.length > 0) {
System.out.println("The " + file.getPath() +
" is not empty!");
}
}
}
}

Result:
The D://Java/file.txt is not empty!

How to get a directory is hidden or not?

Solution:
Following example demonstrates how to get the fact that a file is hidden or not by using file.isHidden() method
of File class.
public class Main {
File file = new File("C:/Demo.txt");
System.out.println(file.isHidden());
}
}

How to print the directory hierarchy?

Saikat Banerjee

Page 52

Solution:
Following example shows how to print the hierarchy of a specified directory using file.getName() and
file.listFiles() method of File class.
public class FileUtil {
public static void main(String[] a)throws IOException{
showDir(1, new File("d:Java"));
}
static void showDir(int indent, File file)
throws IOException {
for (int i = 0; i < indent; i++)
System.out.print('-');
System.out.println(file.getName());
if (file.isDirectory()) {
File[] files = file.listFiles();
for (int i = 0; i < files.length; i++)
showDir(indent + 4, files[i]);
}
}
}

Result:
-Java
-----codes
---------string.txt
---------array.txt
-----tutorial

How to print the last modification time of a directory?

Solution:
Following example demonstrates how to get the last modification time of a directory with the help of
file.lastModified() method of File class.
public class Main {
File file = new File("C://FileIO//demo.txt");
System.out.println("last modifed:" +
new Date(file.lastModified()));
}
}

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Result:
last modifed:10:20:54

The above code sample will produce the following result (as Demo.txt is hidden).
True

How to get the parent directory of a file?

Solution:
Following example shows how to get the parent directory of a file by the use of file.getParent() method of File
class.
public class Main {
File file = new File("C:/File/demo.txt");
String strParentDirectory = file.getParent();
System.out.println("Parent directory is : "
+ strParentDirectory);
}
}

Result:
Parent directory is : File

How to search all files inside a directory?

Solution:
Following example demonstrares how to search and get a list of all files under a specified directory by using
dir.list() method of File class.
public class Main {

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public static void main(String[] argv)
throws Exception {
File dir = new File("directoryName");
String[] children = dir.list();
if (children == null) {
System.out.println("does not exist or
is not a directory");
}
else {
for (int i = 0; i < children.length; i++) {
String filename = children[i];
System.out.println(filename);
}
}
}
}

Result:
sdk
---vehicles
------body.txt
------color.txt
------engine.txt
---ships
------shipengine.txt

How to get the size of a directory?

Solution:
Following example shows how to get the size of a directory with the help of FileUtils.sizeofDirectory(File
Name) method of FileUtils class.
import org.apache.commons.io.FileUtils;
public class Main {
long size = FileUtils.sizeOfDirectory
(new File("C:/Windows"));
System.out.println("Size: " + size + " bytes");
}
}

Result:
Size: 2048 bytes

Saikat Banerjee

Page 55

Java Exception - Programming Examples
Learn how to play with exception in Java programming. Here are most commonly used examples:
1. How to use finally block for catching exceptions?
2. How to use handle the exception heiarchies?
3. How to use handle the exception methods?
4. How to use handle the runtime exceptions?
5. How to use handle the empty stack exception ?
6. How to use catch to handle the exception?
7. How to use catch to handle chained exception?
8. How to use handle the exception with overloaded methods ?
9. How to handle the checked exceptions?
10. How to pass arguments while throwing checked exception?
11. How to handle multiple exceptions (devide by zero)?
12. How to handle multiple exceptions (Array out of bound)?
13. How to use handle the exception with overloaded methods ?
14. How to print stack of the Exception?
15. How to use exceptions with thread?
16. How to create user defined Exception?

How to use finally block for catching exceptions?

Solution:
This example shows how to use finally block to catch runtime exceptions (Illegal Argument Exception) by the
use of e.getMessage().
public class ExceptionDemo2 {
public static void main(String[] argv) {
new ExceptionDemo2().doTheWork();
}
public void doTheWork() {
Object o = null;
for (int i=0; i<5; i++) {
try {
o = makeObj(i);
}
catch (IllegalArgumentException e) {
System.err.println
("Error: ("+ e.getMessage()+").");
return;
}
finally {
System.err.println("All done");
if (o==null)
System.exit(0);
}
System.out.println(o);
}
}
public Object makeObj(int type)
throws IllegalArgumentException {
if (type == 1)

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throw new IllegalArgumentException
("Don't like type " + type);
return new Object();
}
}

Result:
All done
java.lang.Object@1b90b39
Error: (Don't like type 1).
All done

How to handle the exception hierarchies?

Solution:
This example shows how to handle the exception hierarchies by extending Exception class ?
class Animal extends Exception {
}
class Mammel extends Animal {
}
public class Human {
try {
throw new Mammel();
}
catch (Mammel m) {
System.err.println("It is mammel");
}
catch (Annoyance a) {
System.err.println("It is animal");
}
}
}

Result:
It is mammel

How to use handle the exception methods ?

Saikat Banerjee

Page 57

Solution:
This example shows how to handle the exception methods by using System.err.println() method of System
class .
try {
throw new Exception("My Exception");
} catch (Exception e) {
System.err.println("Caught Exception");
System.err.println("getMessage():" + e.getMessage());
System.err.println("getLocalizedMessage():"
+ e.getLocalizedMessage());
System.err.println("toString():" + e);
System.err.println("printStackTrace():");
e.printStackTrace();
}
}

Result:
Caught Exception
getMassage(): My Exception
gatLocalisedMessage(): My Exception
toString():java.lang.Exception: My Exception
print StackTrace():
java.lang.Exception: My Exception
at ExceptionMethods.main(ExceptionMeyhods.java:12)

How to handle the runtime exceptions ?

Solution:
This example shows how to handle the runtime exception in a java programs.
public class NeverCaught {
static void f() {
throw new RuntimeException("From f()");
}
static void g() {
f();
}
g();
}
}

Result:

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Page 58

From f()

How to handle the empty stack exception ?

Solution:
This example shows how to handle the empty stack exception by using s.empty(),s.pop() methods of Stack
class and System.currentTimeMillis()method of Date class .
import java.util.EmptyStackException;
import java.util.Stack;
public class ExceptionalTest {
int count = 1000000;
Stack s = new Stack();
System.out.println("Testing for empty stack");
long s1 = System.currentTimeMillis();
for (int i = 0; i <= count; i++)
if (!s.empty())
s.pop();
long s2 = System.currentTimeMillis();
System.out.println((s2 - s1) + " milliseconds");
System.out.println("Catching EmptyStackException");
s1 = System.currentTimeMillis();
for (int i = 0; i <= count; i++) {
try {
s.pop();
}
catch (EmptyStackException e) {
}
}
s2 = System.currentTimeMillis();
System.out.println((s2 - s1) + " milliseconds");
}
}

Result:
Testing for empty stack
16 milliseconds
Catching EmptyStackException
3234 milliseconds

How to use catch to handle the exception?

Solution:
This example shows how to use catch to handle the exception.

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Page 59

public class Main{
public static void main (String args[]) {
int array[]={20,20,40};
int num1=15,num2=10;
int result=10;
try{
result = num1/num2;
System.out.println("The result is" +result);
for(int i =5;i >=0; i--) {
System.out.println
("The value of array is" +array[i]);
}
}
catch (Exception e) {
System.out.println("Exception occoured : "+e);
}
}
}

Result:
The result is1
Exception occoured : java.lang.ArrayIndexOutOfBoundsException: 5

How to use catch to handle chained exception?

Solution:
This example shows how to handle chained exception using multiple catch blocks.
public class Main{
public static void main (String args[])throws Exception
int n=20,result=0;
try{
result=n/0;
System.out.println("The result is"+result);
}
catch(ArithmeticException ex){
System.out.println
("Arithmetic exception occoured: "+ex);
try {
throw new NumberFormatException();
}
catch(NumberFormatException ex1) {
System.out.println
("Chained exception thrown manually : "+ex1);
}
}
}
}

{

Result:

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Page 60

Arithmetic exception occoured :
java.lang.ArithmeticException: / by zero
Chained exception thrown manually :
java.lang.NumberFormatException

How to handle the exception with overloaded methods ?

Solution:
This example shows how to handle the exception with overloaded methods. You need to have a try catch block
in each method or where the are used.
public class Main {
double method(int i) throws Exception{
return i/0;
}
boolean method(boolean b) {
return !b;
}
static double method(int x, double y) throws Exception
return x + y ;
}
static double method(double x, double y) {
return x + y - 3;
}
Main mn = new Main();
try{
System.out.println(method(10, 20.0));
System.out.println(method(10.0, 20));
System.out.println(method(10.0, 20.0));
System.out.println(mn.method(10));
}
catch (Exception ex){
System.out.println("exception occoure: "+ ex);
}
}
}

{

Result:
30.0
27.0
27.0
exception occoure: java.lang.ArithmeticException: / by zero

Java Data Structure - Programming Examples
Learn how to play with data structure in Java programming. Here are most commonly used examples:
1. How to print summation of n numbers?
2. How to get the first and the last element of a linked list?

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Page 61

3. How to add an element at first and last position of a linked list?
4. How to convert an infix expression to postfix expression?
5. How to implement Queue?
6. How to reverse a string using stack?
7. How to search an element inside a linked list?
8. How to implement stack?
9. How to swap two elements in a vector?
10. How to update a linked list?
11. How to get the maximum element from a vector?
12. How to execute binary search on a vector?
13. How to get elements of a LinkedList?
14. How to delete many elements from a linkedList?

How to print summation of n numbers?

Solution:
Following example demonstrates how to add first n natural numbers by using the concept of stack .
public class AdditionStack {
static int num;
static int ans;
static Stack theStack;
num = 50;
stackAddition();
System.out.println("Sum=" + ans);
}
public static void stackAddition() {
theStack = new Stack(10000);
ans = 0;
while (num > 0) {
theStack.push(num);
--num;
}
while (!theStack.isEmpty()) {
int newN = theStack.pop();
ans += newN;
}
}
}
class Stack {
private int maxSize;
private int[] data;
private int top;
public Stack(int s) {
maxSize = s;
data = new int[maxSize];
top = -1;
}
public void push(int p) {
data[++top] = p;
}

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public int pop() {
return data[top--];
}
public int peek() {
return data[top];
}
public boolean isEmpty() {
return (top == -1);
}
}

Result:
Sum=1225

How to get the first and the last element of a linked list ?

Solution:
Following example shows how to get the first and last element of a linked list with the help of
linkedlistname.getFirst() and linkedlistname.getLast() of LinkedList class.
import java.util.LinkedList;
public class Main {
LinkedList lList = new LinkedList();
lList.add("100");
lList.add("200");
lList.add("300");
lList.add("400");
lList.add("500");
System.out.println("First element of LinkedList is :
" + lList.getFirst());
System.out.println("Last element of LinkedList is :
" + lList.getLast());
}
}

Result:
First element of LinkedList is :100
Last element of LinkedList is :500

How to add an element at first and last position of a linked list?

Saikat Banerjee

Page 63

Solution:
Following example shows how to add an element at the first and last position of a linked list by using addFirst()
and addLast() method of Linked List class.
public class Main {
lList.add("1");
lList.add("2");
lList.add("3");
lList.add("4");
lList.add("5");
System.out.println(lList);
lList.addFirst("0");
lList.addLast("6");
}
}

Result:
1, 2, 3, 4, 5
0, 1, 2, 3, 4, 5
0, 1, 2, 3, 4, 5, 6

How to convert an infix expression to postfix expression?

Solution:
Following example demonstrates how to convert an infix to postfix expression by using the concept of stack.
public class InToPost {
private Stack theStack;
private String input;
private String output = "";
public InToPost(String in) {
input = in;
int stackSize = input.length();
theStack = new Stack(stackSize);
}
public String doTrans() {
for (int j = 0; j < input.length(); j++) {
char ch = input.charAt(j);
switch (ch) {
case '+':
case '-':
gotOper(ch, 1);

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Page 64

break;
case '*':
case '/':
gotOper(ch, 2);
break;
case '(':
theStack.push(ch);
break;
case ')':
gotParen(ch);
break;
default:
output = output + ch;
break;
}
}
output = output + theStack.pop();
}
System.out.println(output);
return output;
}
public void gotOper(char opThis, int prec1) {
char opTop = theStack.pop();
if (opTop == '(') {
theStack.push(opTop);
break;
}
else {
int prec2;
if (opTop == '+' || opTop == '-')
prec2 = 1;
else
prec2 = 2;
if (prec2 < prec1) {
theStack.push(opTop);
break;
}
else
output = output + opTop;
}
}
theStack.push(opThis);
}
public void gotParen(char ch){
char chx = theStack.pop();
if (chx == '(')
break;
else
output = output + chx;
}
}
String input = "1+2*4/5-7+3/6";
String output;
InToPost theTrans = new InToPost(input);
output = theTrans.doTrans();
System.out.println("Postfix is " + output + 'n');
}
class Stack {
private char[] stackArray;

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Page 65

private int top;
public Stack(int max) {
maxSize = max;
stackArray = new char[maxSize];
top = -1;
}
public void push(char j) {
stackArray[++top] = j;
}
public char pop() {
return stackArray[top--];
}
public char peek() {
return stackArray[top];
}
return (top == -1);
}
}
}

Result:
124*5/+7-36/+
Postfix is 124*5/+7-36/+

How to implement Queue ?

Solution:
Following example shows how to implement a queue in an employee structure.
class GenQueue {
private LinkedList list = new LinkedList();
public void enqueue(E item) {
list.addLast(item);
}
public E dequeue() {
return list.poll();
}
public boolean hasItems() {
return !list.isEmpty();
}
public int size() {
return list.size();
}
public void addItems(GenQueue q) {
while (q.hasItems())
list.addLast(q.dequeue());
}
}
public class GenQueueTest {

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Page 66

GenQueue empList;
empList = new GenQueue();
GenQueue hList;
hList = new GenQueue();
hList.enqueue(new HourlyEmployee("T", "D"));
hList.enqueue(new HourlyEmployee("G", "B"));
hList.enqueue(new HourlyEmployee("F", "S"));
empList.addItems(hList);
System.out.println("The employees' names are:");
while (empList.hasItems()) {
Employee emp = empList.dequeue();
System.out.println(emp.firstName + " "
+ emp.lastName);
}
}
}
class Employee {
public String lastName;
public String firstName;
public Employee() {
}
public Employee(String last, String first) {
this.lastName = last;
this.firstName = first;
}
public String toString() {
return firstName + " " + lastName;
}
}
class HourlyEmployee extends Employee {
public double hourlyRate;
public HourlyEmployee(String last, String first) {
super(last, first);
}
}

Result:
The employees' name are:
T D
G B
F S

How to reverse a string using stack ?

Solution:
Following example shows how to reverse a string using stack with the help of user defined method
StringReverserThroughStack().

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Page 67

public class StringReverserThroughStack {
private String input;
private String output;
public StringReverserThroughStack(String in) {
input = in;
}
public String doRev() {
int stackSize = input.length();
Stack theStack = new Stack(stackSize);
for (int i = 0; i < input.length(); i++) {
char ch = input.charAt(i);
theStack.push(ch);
}
output = "";
char ch = theStack.pop();
output = output + ch;
}
return output;
}
String input = "Java Source and Support";
String output;
StringReverserThroughStack theReverser =
new StringReverserThroughStack(input);
output = theReverser.doRev();
System.out.println("Reversed: " + output);
}
class Stack {
private char[] stackArray;
private int top;
public Stack(int max) {
maxSize = max;
stackArray = new char[maxSize];
top = -1;
}
public void push(char j) {
}
public char pop() {
}
public char peek() {
}
return (top == -1);
}
}
}

Result:
JavaStringReversal
Reversed:lasreveRgnirtSavaJ

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Page 68

How to search an element inside a linked list ?

Solution:
Following example demonstrates how to search an element inside a linked list using
linkedlistname.indexof(element) to get the first position of the element and
linkedlistname.Lastindexof(elementname) to get the last position of the element inside the linked list.
public class Main {
lList.add("1");
lList.add("2");
lList.add("3");
lList.add("4");
lList.add("5");
lList.add("2");
System.out.println("First index of 2 is:"+
lList.indexOf("2"));
System.out.println("Last index of 2 is:"+
lList.lastIndexOf("2"));
}
}

Result:
First index of 2 is: 1
Last index of 2 is: 5

How to implement stack?

Solution:
Following example shows how to implement stack by creating user defined push() method for entering
elements and pop() method for retriving elements from the stack.
public class MyStack {
private long[] stackArray;
private int top;
public MyStack(int s) {
maxSize = s;
stackArray = new long[maxSize];
top = -1;
}
public void push(long j) {

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}
public long pop() {
}
public long peek() {
}
return (top == -1);
}
public boolean isFull() {
return (top == maxSize - 1);
}
MyStack theStack = new MyStack(10);
theStack.push(10);
theStack.push(20);
theStack.push(30);
theStack.push(40);
theStack.push(50);
long value = theStack.pop();
System.out.print(value);
System.out.print(" ");
}
}
}

Result:
50 40 30 20 10

How to swap two elements in a vector ?

Solution:
Following example .
public class Main {
Vector v = new Vector();
v.add("1");
v.add("2");
v.add("3");
v.add("4");
v.add("5");
System.out.println(v);
Collections.swap(v, 0, 4);
System.out.println("After swapping");
}

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}

Result:
1 2 3 4 5
After swapping
5 2 3 4 1

How to update a linked list ?

Solution:
Following example demonstrates how to update a linked list by using listname.add() and listname.set() methods
of LinkedList class.
public static void main(String[] a) {
LinkedList officers = new LinkedList();
officers.add("B");
officers.add("B");
officers.add("T");
officers.add("H");
officers.add("P");
System.out.println(officers);
officers.set(2, "M");
System.out.println(officers);
}
}

Result:
BBTHP
BBMHP

How to get the maximum element from a vector ?

Solution:
Following example demonstrates how to get the maximum element of a vector by using v.add() method of
Vector class and Collections.max() method of Collection class.

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public class Main {
v.add(new Double("3.4324"));
Object obj = Collections.max(v);
System.out.println("The max element is:"+obj);
}
}

Result:
The max element is: 3.4324

How to execute binary search on a vector ?

Solution:
Following example how to execute binary search on a vector with the help of v.add() method of Vector class
and sort.Collection() method of Collection class.
public class Main {
v.add("X");
v.add("M");
v.add("D");
v.add("A");
v.add("O");
Collections.sort(v);
int index = Collections.binarySearch(v, "D");
System.out.println("Element found at : " + index);
}
}

Result:
[A, D, M, O, X]
Element found at : 1

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Page 72

How to get elements of a LinkedList?

Solution:
Following example demonstrates how to get elements of LinkedList using top() & pop() methods.
import java.util.*;
public class Main {
private LinkedList list = new LinkedList();
public void push(Object v) {
list.addFirst(v);
}
public Object top() {
return list.getFirst();
}
public Object pop() {
return list.removeFirst();
}
Main stack = new Main();
for (int i = 30; i < 40; i++)
stack.push(new Integer(i));
System.out.println(stack.top());
System.out.println(stack.pop());
}
}

Result:
39
39
38
37

How to delete many elements from a linkedList?

Solution:
Following example demonstrates how to delete many elements of linkedList using Clear() method.
import java.util.*;
public class Main {
lList.add("1");
lList.add("8");

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lList.add("6");
lList.add("4");
lList.add("5");
lList.subList(2, 4).clear();
}
}

Result:
[one, two, three, four, five]
[one, two, three, Replaced, five]

Java Collection - Programming Examples
Learn how to play with collections in Java programming. Here are most commonly used examples:
1. How to convert an array into a collection?
2. How to compare elements in a collection?
3. How to convert a collection into an array?
4. How to print a collection?
5. How to make a collection read-only?
6. How to remove a specific element from a collection?
7. How to reverse a collection?
8. How to shuffle the elements of a collection?
9. How to get the size of a collection?
10. How to iterate through elements of HashMap?
11. How to use different types of Collections?
12. How to use enumeration to display contents of HashTable?
13. How to get Set view of Keys from Java Hashtable?
14. How to find min & max of a List?
15. How to find a sublist in a List?
16. How to replace an element in a list?
17. How to rotate elements of the List?

How to convert an array into a collection?

Solution:
Following example demonstrates to convert an array into a collection Arrays.asList(name) method of Java Util
class.
import java.util.*;
import java.io.*;
public class ArrayToCollection{
public static void main(String args[])

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throws IOException{
(new InputStreamReader(System.in));
System.out.println("How many elements
you want to add to the array: ");
int n = Integer.parseInt(in.readLine());
String[] name = new String[n];
for(int i = 0; i < n; i++){
name[i] = in.readLine();
}
List list = Arrays.asList(name);
for(String li: list){
String str = li;
System.out.print(str + " ");
}
}
}

Result:
How many elements you want to add to the array:
red white green
red white green

How to compare elements in a collection ?

Solution:
Following example compares the element of a collection by converting a string into a treeset using
Collection.min() and Collection.max() methods of Collection class.
import java.util.Set;
import java.util.TreeSet;
class MainClass {
String[] coins = { "Penny", "nickel", "dime",
"Quarter", "dollar" };
Set set = new TreeSet();
for (int i = 0; i < coins.length; i++)
set.add(coins[i]);
System.out.println(Collections.min(set));
System.out.println(Collections.min(set,
String.CASE_INSENSITIVE_ORDER));
for(int i=0;i< =10;i++)
System.out.print(-);
System.out.println(Collections.max(set));
System.out.println(Collections.max(set,
String.CASE_INSENSITIVE_ORDER));
}

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}

Result:
Penny
dime
---------nickle
Quarter

How to change a collection to an array?

Solution:
Following example shows how to convert a collection to an array by using list.add() and list.toArray() method
of Java Util class.
import java.util.*;
public class CollectionToArray{
List list = new ArrayList();
list.add("This ");
list.add("is ");
list.add("a ");
list.add("good ");
list.add("program.");
String[] s1 = list.toArray(new String[0]);
for(int i = 0; i < s1.length; ++i){
String contents = s1[i];
System.out.print(contents);
}
}
}

Result:
This is a good program.

How to print a collection?

Solution:
Following example how to print a collection by using tMap.keySet(),tMap.values() and tMap.firstKey()
methods of Java Util class .

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import java.util.*;
public class TreeExample{
System.out.println("Tree Map Example!n");
TreeMap tMap = new TreeMap();
tMap.put(1, "Sunday");
tMap.put(2, "Monday");
tMap.put(3, "Tuesday");
tMap.put(4, "Wednesday");
tMap.put(5, "Thursday");
tMap.put(6, "Friday");
tMap.put(7, "Saturday");
System.out.println("Keys of tree map: "
+ tMap.keySet());
System.out.println("Values of tree map: "
+ tMap.values());
System.out.println("Key: 5 value: " + tMap.get(5)+ "n");
System.out.println("First key: " + tMap.firstKey()
+ " Value: "
+ tMap.get(tMap.firstKey()) + "n");
System.out.println("Last key: " + tMap.lastKey()
+ " Value: "+ tMap.get(tMap.lastKey()) + "n");
System.out.println("Removing first data: "
+ tMap.remove(tMap.firstKey()));
System.out.println("Now the tree map Keys: "
+ tMap.keySet());
System.out.println("Now the tree map contain: "
+ tMap.values() + "n");
System.out.println("Removing last data: "
+ tMap.remove(tMap.lastKey()));
System.out.println("Now the tree map Keys: "
+ tMap.keySet());
System.out.println("Now the tree map contain: "
+ tMap.values());
}
}

Result:
C:collection>javac TreeExample.java
C:collection>java TreeExample
Tree Map Example!
Keys of tree map: [1, 2, 3, 4, 5, 6, 7]
Values of tree map: [Sunday, Monday, Tuesday, Wednesday,
Thursday, Friday, Saturday]
Key: 5 value: Thursday
First key: 1 Value: Sunday
Last key: 7 Value: Saturday
Removing first data: Sunday
Now the tree map Keys: [2, 3, 4, 5, 6, 7]
Now the tree map contain: [Monday, Tuesday, Wednesday,
Thursday, Friday, Saturday]
Removing last data: Saturday

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Now the tree map Keys: [2, 3, 4, 5, 6]
Now the tree map contain: [Monday, Tuesday, Wednesday,
Thursday, Friday]
C:collection>

How to make a collection read-only ?

Solution:
Following example shows how to make a collection read-only by using Collections.unmodifiableList() method
of Collection class.
import
import
import
import
import
import
import
import

java.util.ArrayList;
java.util.Arrays;
java.util.Collections;
java.util.HashMap;
java.util.HashSet;
java.util.List;
java.util.Map;
java.util.Set;

public class Main {
throws Exception {
List stuff = Arrays.asList(new String[] { "a", "b" });
List list = new ArrayList(stuff);
list = Collections.unmodifiableList(list);
try {
list.set(0, "new value");
}
catch (UnsupportedOperationException e) {
}
Set set = new HashSet(stuff);
set = Collections.unmodifiableSet(set);
Map map = new HashMap();
map = Collections.unmodifiableMap(map);
System.out.println("Collection is read-only now.");
}
}

Result:
Collection is read-only now.

How to remove a specific element from a collection?

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Solution:
Following example demonstrates how to remove a certain element from a collection with the help of
collection.remove() method of Collection class.
import java.util.*;
public class CollectionTest {
public static void main(String [] args) {
System.out.println( "Collection Example!n" );
int size;
HashSet collection = new HashSet ();
String str1 = "Yellow", str2 = "White", str3 =
"Green", str4 = "Blue";
Iterator iterator;
collection.add(str1);
System.out.print("Collection data: ");
iterator = collection.iterator();
while (iterator.hasNext()){
System.out.print(iterator.next() + " ");
}
collection.remove(str2);
System.out.println("After removing [" + str2 + "]n");
System.out.print("Now collection data: ");
}
size = collection.size();
System.out.println("Collection size: " + size + "n");
}
}

Result:
Collection Example!
Collection data: Blue White Green Yellow
After removing [White]
Now collection data: Blue Green Yellow
Collection size: 3

How to reverse a collection ?

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Solution:
Following example demonstratres how to reverse a collection with the help of listIterator() and
Collection.reverse() methods of Collection and Listiterator class .
import
import
import
import

java.util.Collections;
java.util.List;
java.util.ListIterator;

class UtilDemo3 {
String[] coins = { "A", "B", "C", "D", "E" };
List l = new ArrayList();
for (int i = 0; i < coins.length; i++)
l.add(coins[i]);
ListIterator liter = l.listIterator();
System.out.println("Before reversal");
while (liter.hasNext())
System.out.println(liter.next());
Collections.reverse(l);
liter = l.listIterator();
System.out.println("After reversal");
while (liter.hasNext())
System.out.println(liter.next());
}
}

Result:
Before reversal
A
B
C
D
E
After reversal
E
D
C
B
A

How to shuffle the elements of a collection ?

Solution:
Following example how to shuffle the elements of a collection with the help of Collections.shuffle() method of
Collections class.
import java.util.List;

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public class Main {
throws Exception {
String[] alpha = { "A", "E", "I", "O", "U" };
List list = new ArrayList(alpha);
Collections.shuffle(list);
System.out.println("list");
}
}

Result:
I
O
A
U
E

How to get size of a collection?

Solution:
Following example shows how to get the size of a collection by the use of collection.add() to add new data and
collection.size() to get the size of the collection of Collections class.
import java.util.*;
public class CollectionTest {
public static void main(String [] args) {
System.out.println( "Collection Example!n" );
int size;
HashSet collection = new HashSet ();
String str1 = "Yellow", str2 = "White", str3 =
"Green", str4 = "Blue";
Iterator iterator;
System.out.print("Collection data: ");
}
size = collection.size();
if (collection.isEmpty()){
System.out.println("Collection is empty");
}
else{
System.out.println( "Collection size: " + size);
}

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}
}

Result:
Collection Example!
Collection data: Blue White Green Yellow
Collection size: 4

How to iterate through elements of HashMap?

Solution:
Following example uses iterator Method of Collection class to iterate through the HashMap.
import java.util.*;
public class Main {
HashMap< String, String> hMap =
new HashMap< String, String>();
hMap.put("1", "1st");
hMap.put("2", "2nd");
hMap.put("3", "3rd");
Collection cl = hMap.values();
Iterator itr = cl.iterator();
while (itr.hasNext()) {
System.out.println(itr.next());
}
}
}

Result:
3rd
2nd
1st

How to use different types of Collections?

Solution:
Following example uses different types of collection classes and adds an element in those collections.

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import
import
import
import
import
import

java.util.Map;
java.util.Set;
java.util.SortedMap;
java.util.SortedSet;
java.util.TreeMap;
java.util.TreeSet;

import
import
import
import
import
import
import
import
import

java.util.Collection;
java.util.HashMap;
java.util.HashSet;
java.util.Iterator;
java.util.LinkedHashMap;
java.util.LinkedHashSet;
java.util.LinkedList;
java.util.List;

public class Main {
List lnkLst = new LinkedList();
lnkLst.add("element1");
displayAll(lnkLst);
List aryLst = new ArrayList();
aryLst.add("x");
aryLst.add("y");
aryLst.add("z");
aryLst.add("w");
displayAll(aryLst);
Set hashSet = new HashSet();
hashSet.add("set1");
displayAll(hashSet);
SortedSet treeSet = new TreeSet();
treeSet.add("1");
treeSet.add("2");
treeSet.add("3");
treeSet.add("4");
displayAll(treeSet);
LinkedHashSet lnkHashset = new LinkedHashSet();
lnkHashset.add("one");
lnkHashset.add("two");
lnkHashset.add("three");
lnkHashset.add("four");
displayAll(lnkHashset);
Map ma p1 = new HashMap();
map1.put("key1", "J");
map1.put("key2", "K");
map1.put("key3", "L");
map1.put("key4", "M");
displayAll(map1.keySet());
displayAll(map1.values());
SortedMap map2 = new TreeMap();
map2.put("key1", "JJ");
map2.put("key2", "KK");
map2.put("key3", "LL");
map2.put("key4", "MM");
LinkedHashMap map3 = new LinkedHashMap();

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map3.put("key1", "JJJ");
map3.put("key2", "KKK");
map3.put("key3", "LLL");
map3.put("key4", "MMM");
}
static void displayAll(Collection col) {
Iterator itr = col.iterator();
String str = (String) itr.next();
System.out.print(str + " ");
}
}
}

Result:
element1 element2 element3 element4
x y z w
set1 set2 set3 set4
1 2 3 4
one two three four
key4 key3 key2 key1
M L K J
key1 key2 key3 key4
JJ KK LL MM
key1 key2 key3 key4
JJJ KKK LLL MMM

How to use enumeration to display contents of HashTable?

Solution:
Following example uses hasMoreElements & nestElement Methods of Enumeration Class to display the
contents of the HashTable.
import java.util.Enumeration;
import java.util.Hashtable;
public class Main {
Hashtable ht = new Hashtable();
ht.put("1", "One");
ht.put("2", "Two");
ht.put("3", "Three");
Enumeration e = ht.elements();
While (e.hasMoreElements()){
System.out.println(e.nextElement());
}
}
}

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Result:
Three
Two
One

How to set view of Keys from Java Hashtable?

Solution:
Following example uses keys() method to get Enumeration of Keys of the Hashtable.
import java.util.Enumeration;
import java.util.Hashtable;
public class Main {
Hashtable ht = new Hashtable();
ht.put("1", "One");
ht.put("2", "Two");
ht.put("3", "Three");
Enumeration e = ht.keys();
while (e.hasMoreElements()){
System.out.println(e.nextElement());
}
}
}

Result:
3
2
1

How to find min & max of a List?

Solution:
Following example uses min & max Methods to find minimum & maximum of the List.
import java.util.*;
public class Main {
List list = Arrays.asList("one Two three Four five six

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one three Four".split(" "));
System.out.println(list);
System.out.println("max: " + Collections.max(list));
System.out.println("min: " + Collections.min(list));
}
}

Result:
[one, Two, three, Four, five, six, one, three, Four]
max: three
min: Four

How to find a sublist in a List?

Solution:
Following example uses indexOfSubList() & lastIndexOfSubList() to check whether the sublist is there in the
list or not & to find the last occurance of the sublist in the list.
import java.util.*;
public class Main {
List list = Arrays.asList("one Two three Four five
six one three Four".split(" "));
System.out.println("List :"+list);
List sublist = Arrays.asList("three Four".split(" "));
System.out.println("SubList :"+sublist);
System.out.println("indexOfSubList: "
+ Collections.indexOfSubList(list, sublist));
System.out.println("lastIndexOfSubList: "
+ Collections.lastIndexOfSubList(list, sublist));
}
}

Result:
List :[one, Two, three, Four, five, six, one, three, Four]
SubList :[three, Four]
indexOfSubList: 2
lastIndexOfSubList: 7

How to replace an element in a list

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Solution:
Following example uses replaceAll() method to replace all the occurance of an element with a different element
in a list.
import java.util.*;
public class Main {
List list = Arrays.asList("one Two three Four five six
one three Four".split(" "));
Collections.replaceAll(list, "one", "hundread");
System.out.println("replaceAll: " + list);
}
}

Result:
List :[one, Two, three, Four, five, six, one, three, Four]
replaceAll: [hundread, Two, three, Four, five, six,
hundread, three, Four]

How to rotate elements of the List?

Solution:
Following example uses rotate() method to rotate elements of the list depending on the 2nd argument of the
method.
import java.util.*;
public class Main {
List list = Arrays.asList("one Two three Four five
six".split(" "));
Collections.rotate(list, 3);
System.out.println("rotate: " + list);
}
}

Result:
List :[one, Two, three, Four, five, six]
rotate: [Four, five, six, one, Two, three]

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Java Network - Programming Examples
Learn how to modify networks in Java programming. Here are most commonly used examples:
1. How to change the host name to its specific IP address?
2. How to get connected with web server?
3. How to check a file is modified at a server or not?
4. How to create a multithreaded server?
5. How to get the file size from the server?
6. How to make a socket displaying message to a single client?
7. How to make a srever to allow the connection to the socket 6123?
8. How to get the parts of an URL?
9. How to get the date of URL connection?
10. How to read and download a webpage?
11. How to find hostname from IP Address?
12. How to determine IP Address & hostname of Local Computer?
13. How to check whether a port is being used or not?
14. How to find proxy settings of a System?
15. How to create a socket at a specific port?

How to split a string into a number of substrings ?

Solution:
Following example shows how to change the host name to its specific IP address with the help of
InetAddress.getByName() method of net.InetAddress class.
import java.net.InetAddress;
import java.net.UnknownHostException;
public class GetIP {
InetAddress address = null;
try {
address = InetAddress.getByName
("www.javatutorial.com");
}
catch (UnknownHostException e) {
System.exit(2);
}
System.out.println(address.getHostName() + "="
+ address.getHostAddress());
System.exit(0);
}
}

Result:

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http://www.sbdsisaikat.com = 123.14.2.35

How to get connected with web server?

Solution:
Following example demonstrates how to get connected with web server by using sock.getInetAddress() method
of net.Socket class.
import java.net.Socket;
public class WebPing {
try {
InetAddress addr;
Socket sock = new Socket("www.javatutorial.com", 80);
addr = sock.getInetAddress();
System.out.println("Connected to " + addr);
sock.close();
} catch (java.io.IOException e) {
System.out.println("Can't connect to " + args[0]);
System.out.println(e);
}
}
}

Result:
Connected to http://www.sbdsisaikat.com/102.32.56.14

How to check a file is modified at a server or not?

Solution:
Following example shows How to check a file is modified at a server or not.
import java.net.URL;
import java.net.URLConnection;
public class Main {
throws Exception {
URL u = new URL("http://127.0.0.1/java.bmp");
URLConnection uc = u.openConnection();
uc.setUseCaches(false);
long timestamp = uc.getLastModified();

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System.out.println("The last modification time
of java.bmp is :"+timestamp);
}
}

Result:
The last modification time of java.bmp is :24 May 2009 12:14:50

How to create a multithreaded server?

Solution:
Following example demonstrates how to create a multithreaded server by using ssock.accept() method of
Socket class and MultiThreadServer(socketname) method of ServerSocket class.
import
import
import
import

java.io.IOException;
java.io.PrintStream;
java.net.ServerSocket;
java.net.Socket;

public class MultiThreadServer implements Runnable {
Socket csocket;
MultiThreadServer(Socket csocket) {
this.csocket = csocket;
}
throws Exception {
ServerSocket ssock = new ServerSocket(1234);
System.out.println("Listening");
while (true) {
Socket sock = ssock.accept();
System.out.println("Connected");
new Thread(new MultiThreadServer(sock)).start();
}
}
public void run() {
try {
PrintStream pstream = new PrintStream
(csocket.getOutputStream());
for (int i = 100; i >= 0; i--) {
pstream.println(i +
" bottles of beer on the wall");
}
pstream.close();
csocket.close();
}
System.out.println(e);
}
}
}

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Result:
Listening
Connected

How to get the file size from the server?

Solution:
Following example demonstrates How to get the file size from the server.
import java.net.URLConnection;
public class Main {
throws Exception {
int size;
URL url = new URL("http://www.server.com");
URLConnection conn = url.openConnection();
size = conn.getContentLength();
if (size < 0)
System.out.println("Could not determine file size.");
else
System.out.println("The size of the file is = "
+size + "bytes");
conn.getInputStream().close();
}
}

Result:
The size of The file is = 16384 bytes

How to make a socket displaying message to a single client?

Solution:
Following example demonstrates how to make a socket displaying message to a single client with the help of
ssock.accept() method of Socket class.
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;

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public class BeerServer {
throws Exception {
ServerSocket ssock = new ServerSocket(1234);
Socket sock = ssock.accept();
ssock.close();
PrintStream ps = new PrintStream
(sock.getOutputStream());
for (int i = 10; i >= 0; i--) {
ps.println(i +
" from Java Source and Support.");
}
ps.close();
sock.close();
}
}

Result:
Listening
10 from Java Source and Support

How to make a srever to allow the connection to the socket 6123?

Solution:
Following example shows how to make a srever to allow the connection to the socket 6123 by using
server.accept() method of ServerSocket class andb sock.getInetAddress() method of Socket class.
import
import
import
import

java.net.InetAddress;
java.net.ServerSocket;
java.net.Socket;

public class SocketDemo {
try {
ServerSocket server = new ServerSocket(6123);
while (true) {
Socket sock = server.accept();
InetAddress addr = sock.getInetAddress();
System.out.println("Connection made to "

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+ addr.getHostName()
+ " (" + addr.getHostAddress() + ")");
pause(5000);
sock.close();
}
}
System.out.println("Exception detected: " + e);
}
}
private static void pause(int ms) {
try {
Thread.sleep(ms);
}
catch (InterruptedException e) {
}
}
}

Result:
Listening
Terminate batch job (Y/N)? n
Connection made to 112.63.21.45

How to get the parts of an URL?

Solution:
Following example shows how to get the parts of an URL with the help of url.getProtocol() ,url.getFile()
method etc. of net.URL class.
public class Main {
throws Exception {
URL url = new URL(args[0]);
System.out.println("URL is " + url.toString());
System.out.println("protocol is "
+ url.getProtocol());
System.out.println("file name is " + url.getFile());
System.out.println("host is " + url.getHost());
System.out.println("path is " + url.getPath());
System.out.println("port is " + url.getPort());
System.out.println("default port is "
+ url.getDefaultPort());
}
}

Result:

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URL is http://www.server.com
protocol is TCP/IP
file name is java_program.txt
host is 122.45.2.36
path is
port is 2
default port is 1

How to get the date of URL connection?

Solution:
Following example demonstrates how to get the date of URL connection by using httpCon.getDate() method of
HttpURLConnection class.
import java.net.HttpURLConnection;
public class Main{
throws Exception {
URL url = new URL("http://www.google.com");
HttpURLConnection httpCon =
(HttpURLConnection) url.openConnection();
long date = httpCon.getDate();
if (date == 0)
System.out.println("No date information.");
else
System.out.println("Date: " + new Date(date));
}
}

Result:
Date:05.26.2009

How to read and download a webpage?

Solution:
Following example shows how to read and download a webpage URL() constructer of net.URL class.
import
import
import
import
import

java.io.BufferedReader;
java.io.BufferedWriter;
java.io.FileWriter;
java.io.InputStreamReader;
java.net.URL;

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public class Main {
throws Exception {
URL url = new URL("http://www.google.com");
BufferedReader reader = new BufferedReader
(new InputStreamReader(url.openStream()));
BufferedWriter writer = new BufferedWriter
(new FileWriter("data.html"));
String line;
while ((line = reader.readLine()) != null) {
System.out.println(line);
writer.write(line);
writer.newLine();
}
reader.close();
writer.close();
}
}

Result:
Welcome to Java Tutorial
Here we have plenty of examples for you!
Come and Explore Java!

How to find hostname from IP Address?

Solution:
Following example shows how to change the host name to its specific IP address with the help of
InetAddress.getByName() method of net.InetAddress class.
public class Main {
InetAddress addr = InetAddress.getByName("74.125.67.100");
System.out.println("Host name is: "+addr.getHostName());
System.out.println("Ip address is: "+ addr.getHostAddress());
}
}

Result:
http://www.sbdsisaikat.com = 123.14.2.35

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How to determine IP Address & hostname of Local Computer?

Solution:
Following example shows how to find local IP Address & Hostname of the system using getLocalAddress()
method of InetAddress class.
public class Main {
throws Exception {
InetAddress addr = InetAddress.getLocalHost();
System.out.println("Local HostAddress:
"+addr.getHostAddress());
String hostname = addr.getHostName();
System.out.println("Local host name: "+hostname);
}
}

Result:
Local HostAddress: 192.168.1.4
Local host name: saikat

How to check whether a port is being used or not?

Solution:
Following example shows how to check whether any port is being used as a server or not by creating a socket
object.
import java.net.*;
import java.io.*;
public class Main {
Socket Skt;
String host = "localhost";
if (args.length > 0) {
host = args[0];
}
for (int i = 0; i < 1024; i++) {
try {
System.out.println("Looking for "+ i);
Skt = new Socket(host, i);
System.out.println("There is a server on port "
+ i + " of " + host);

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}
System.out.println("Exception occured"+ e);
break;
}
}
}
}
}

Result:
Looking
Looking
Looking
Looking
Looking

for
for
for
for
for

0
1
2
3
4. . .

How to find proxy settings of a System?

Solution:
Following example shows how to find proxy settings & create a proxy connection on a system using put
method of systemSetting & getResponse method of HttpURLConnection class.
import
import
import
import
import
import
import

java.net.HttpURLConnection;
java.net.URL;
java.util.Properties;
java.net.InetSocketAddress;
java.net.Proxy;
java.net.ProxySelector;
java.net.URI;

public class Main{
public static void main(String s[])
throws Exception{
try {
Properties systemSettings =
System.getProperties();
systemSettings.put("proxySet", "true");
systemSettings.put("http.proxyHost",
"proxy.mycompany1.local");
systemSettings.put("http.proxyPort", "80");
URL u = new URL("http://www.google.com");
HttpURLConnection con = (HttpURLConnection)
u.openConnection();
System.out.println(con.getResponseCode() +
" : " + con.getResponseMessage());
System.out.println(con.getResponseCode() ==
HttpURLConnection.HTTP_OK);
}
catch (Exception e) {
e.printStackTrace();

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System.out.println(false);
}
System.setProperty("java.net.useSystemProxies",
"true");
Proxy proxy = (Proxy) ProxySelector.getDefault().
select(new URI("http://www.yahoo.com/")).iterator().
next();;
System.out.println("proxy hostname : " + proxy.type());
InetSocketAddress addr = (InetSocketAddress)
proxy.address();
if (addr == null) {
System.out.println("No Proxy");
}
else {
System.out.println("proxy hostname : "
+ addr.getHostName());
System.out.println("proxy port : "
+ addr.getPort());
}
}
}

Result:
200 :
true
proxy
proxy
proxy

OK
hostname : HTTP
hostname : proxy.mycompany1.local
port : 80

How to create a socket at a specific port?

Solution:
Following example shows how to sing Socket constructor of Socket class.And also get Socket details using
getLocalPort() getLocalAddress , getInetAddress() & getPort() methods.
import
import
import
import
import

java.net.InetAddress;
java.net.Socket;
java.net.SocketException;
java.net.UnknownHostException;

public class Main {
try {
InetAddress addr =
InetAddress.getByName("74.125.67.100");
Socket theSocket = new Socket(addr, 80);
System.out.println("Connected to "
+ theSocket.getInetAddress()
+ " on port " + theSocket.getPort() + " from port "
+ theSocket.getLocalPort() + " of "
+ theSocket.getLocalAddress());

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}
System.err.println("I can't find " + e );
}
catch (SocketException e) {
System.err.println("Could not connect to " +e );
}
System.err.println(e);
}
}
}

Result:
Connected to /74.125.67.100 on port 80 from port
2857 of /192.168.1.4

Java Threading - Programming Examples
Learn how to use threads in Java programming. Here are most commonly used examples:
1. How to check a thread is alive or not?
2. How to check a thread has stop or not?
3. How to solve deadlock using thread?
4. How to get the priorities of running threads?
5. How to monitor a thread's status?
6. How to get the name of a running thread?
7. How to solve the producer consumer problem using thread?
8. How to set the priority of a thread?
9. How to stop a thread?
10. How to suspend a thread for a while?
11. How to get the Id of the running thread?
12. How to check priority level of a thread?
13. How to display all running Thread?
14. How to display thread status?
15. How to interrupt a running Thread?

How to check a thread is alive or not?

Solution:
Following example demonstrates how to check a thread is alive or not by extending Threda class and using
currentThread() method.
public class TwoThreadAlive extends Thread {
public void run() {
for (int i = 0; i < 10; i++) {

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printMsg();
}
}
public void printMsg() {
Thread t = Thread.currentThread();
String name = t.getName();
System.out.println("name=" + name);
}
TwoThreadAlive tt = new TwoThreadAlive();
tt.setName("Thread");
System.out.println("before start(),
tt.isAlive()=" + tt.isAlive());
tt.start();
System.out.println("just after start(),
for (int i = 0; i < 10; i++) {
tt.printMsg();
}
System.out.println("The end of main(),
}
}

Result:
before start(),tt.isAlive()=false
just after start(), tt.isAlive()=true
name=main
name=main
name=main
name=main
name=main
name=Thread
name=Thread
name=Thread
name=Thread
name=Thread
name=Thread
name=Thread
name=main
name=main
The end of main().tt.isAlive()=false

How to check a thread has stop or not?

Solution:
Following example demonstrates how to check a thread has stop or not by checking with isAlive() method.
public class Main {
throws Exception {

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Thread thread = new MyThread();
thread.start();
if (thread.isAlive()) {
System.out.println("Thread has not finished");
}
else {
System.out.println("Finished");
}
long delayMillis = 5000;
thread.join(delayMillis);
if (thread.isAlive()) {
System.out.println("thread has not finished");
}
else {
System.out.println("Finished");
}
thread.join();
}
}
class MyThread extends Thread {
boolean stop = false;
public void run() {
while (true) {
if (stop) {
return;
}
}
}
}

Result:
Thread has not finished
Finished

How to solve deadlock using thread?

Solution:
Following example demonstrates how to solve deadlock using the concept of thread.
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.locks.*;
public class DeadlockDetectingLock extends ReentrantLock {
private static List deadlockLocksRegistry
= new ArrayList();
private static synchronized void
registerLock(DeadlockDetectingLock ddl) {
if (!deadlockLocksRegistry.contains(ddl))
deadlockLocksRegistry.add(ddl);
}

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unregisterLock(DeadlockDetectingLock ddl) {
if (deadlockLocksRegistry.contains(ddl))
deadlockLocksRegistry.remove(ddl);
}
private List hardwaitingThreads = new ArrayList();
markAsHardwait(List l, Thread t) {
if (!l.contains(t))
l.add(t);
}
freeIfHardwait(List l, Thread t) {
if (l.contains(t))
l.remove(t);
}
private static Iterator getAllLocksOwned(Thread t) {
DeadlockDetectingLock current;
ArrayList results = new ArrayList();
Iterator itr = deadlockLocksRegistry.iterator();
current = (DeadlockDetectingLock) itr.next();
if
(current.getOwner() == t)
results.add(current);
}
return results.iterator();
}
private static Iterator
getAllThreadsHardwaiting(DeadlockDetectingLock l) {
return l.hardwaitingThreads.iterator();
}
private static synchronized boolean canThreadWaitOnLock
(Thread t,DeadlockDetectingLock l) {
Iterator locksOwned = getAllLocksOwned(t);
while (locksOwned.hasNext()) {
DeadlockDetectingLock current
= (DeadlockDetectingLock) locksOwned.next();
if (current == l)
return false;
Iterator waitingThreads
= getAllThreadsHardwaiting(current);
while (waitingThreads.hasNext()) {
Thread otherthread = (Thread) waitingThreads.next();
if (!canThreadWaitOnLock(otherthread, l)) {
return false;
}
}
}
return true;
}
public DeadlockDetectingLock() {
this(false, false);
}
public DeadlockDetectingLock(boolean fair) {
this(fair, false);
}
private boolean debugging;
public DeadlockDetectingLock(boolean fair, boolean debug) {

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super(fair);
debugging = debug;
registerLock(this);
}
public void lock() {
if (isHeldByCurrentThread()) {
if (debugging)
System.out.println("Already Own Lock");
super.lock();
freeIfHardwait(hardwaitingThreads,
Thread.currentThread());
return;
}
markAsHardwait(hardwaitingThreads,
if (canThreadWaitOnLock(Thread.currentThread(), this)) {
if (debugging)
System.out.println("Waiting For Lock");
super.lock();
if (debugging)
System.out.println("Got New Lock");
}
else {
throw new DeadlockDetectedException("DEADLOCK");
}
}
public void lockInterruptibly() throws InterruptedException {
lock();
}
locks.
public class DeadlockDetectingCondition implements Condition {
Condition embedded;
protected DeadlockDetectingCondition(ReentrantLock lock,
Condition embedded) {
this.embedded = embedded;
}
Public void await() throws InterruptedException {
try {
embedded.await();
}
finally {
}
}
public void awaitUninterruptibly() {
embedded.awaitUninterruptibly();
}
public long awaitNanos(long nanosTimeout)
throws InterruptedException {
try {

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return embedded.awaitNanos(nanosTimeout);
}
finally {
}
}
public boolean await(long time, TimeUnit unit)
try {
return embedded.await(time, unit);
}
finally {
}
}
public boolean awaitUntil(Date deadline)
try {
return embedded.awaitUntil(deadline);
}
finally {
}
}
public void signal() {
embedded.signal();
}
public void signalAll() {
embedded.signalAll();
}
}
public Condition newCondition() {
return new DeadlockDetectingCondition(this,
super.newCondition());
}
private static Lock a = new DeadlockDetectingLock(false, true);
private static Lock b = new DeadlockDetectingLock(false, true);
private static Lock c = new DeadlockDetectingLock(false, true);
private static Condition wa = a.newCondition();
private static Condition wb = b.newCondition();
private static Condition wc = c.newCondition();
private static void delaySeconds(int seconds) {
try {
Thread.sleep(seconds * 1000);
}
catch (InterruptedException ex) {
}
}
private static void awaitSeconds(Condition c, int seconds) {

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try {
c.await(seconds, TimeUnit.SECONDS);
}
catch (InterruptedException ex) {
}
}
private static void testOne() {
new Thread(new Runnable() {
public void run() {
System.out.println("thread
a.lock();
delaySeconds(2);
b.lock();
delaySeconds(2);
a.unlock();
b.unlock();
}
}).start();
public void run() {
b.lock();
delaySeconds(2);
a.lock();
delaySeconds(2);
a.unlock();
b.unlock();
}
}).start();
}
private static void testTwo() {
public void run() {
a.lock();
delaySeconds(2) ;
b.lock();
delaySeconds(10);
a.unlock();
b.unlock();
}
}).start();
public void run() {
b.lock();
delaySeconds(2);
c.lock();
delaySeconds(10);
b.unlock();
c.unlock();
}
}).start();
public void run() {
c.lock();
delaySeconds(4);

Saikat Banerjee

one grab a");
one grab b");

two grab b");
two grab a");

one grab a");
one grab b");

two grab b");
two grab c");

three grab c");
three grab a");

Page 105

a.lock();
delaySeconds(10);
c.unlock();
a.unlock();
}
}).start();
}
private static void testThree() {
public void run() {
b.lock();
a.lock();
delaySeconds(2);
awaitSeconds(wb, 10);
a.unlock();
b.unlock();
}
}).start();
public void run() {
delaySeconds(1);
b.lock();
a.lock();
delaySeconds(10);
b.unlock();
c.unlock();
}
}).start();
}

one grab b");
one grab a");
one waits on b");

two grab b");
two grab a");

int test = 1;
if (args.length > 0)
test = Integer.parseInt(args[0]);
switch (test) {
case 1:
testOne();
break;
case 2:
testTwo();
break;
case 3:
testThree();
break;
default:
System.err.println("usage: java
DeadlockDetectingLock [ test# ]");
}
delaySeconds(60);
System.out.println("--- End Program ---");
System.exit(0);
}
}
class DeadlockDetectedException extends RuntimeException {
public DeadlockDetectedException(String s) {
super(s);
}
}

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Result:
thread one grab a
Waiting For Lock
Got New Lock
thread two grab b
Waiting For Lock
Got New Lock
thread one grab b
Waiting For Lock
thread two grab a
Exception in thread "Thread-1"
DeadlockDetectedException:DEADLOCK
at DeadlockDetectingLock.
lock(DealockDetectingLock.java:152)
at java.lang.Thread.run(Thread.java:595)

How to get the priorities of running threads?

Solution:
Following example prints the priority of the running threads by using setPriority() method .
public class SimplePriorities extends Thread {
private int countDown = 5;
private volatile double d = 0;
public SimplePriorities(int priority) {
setPriority(priority);
start();
}
return super.toString() + ": " + countDown;
}
public void run() {
while(true) {
for(int i = 1; i < 100000; i++)
d = d + (Math.PI + Math.E) / (double)i;
System.out.println(this);
if(--countDown == 0) return;
}
}
new SimplePriorities(Thread.MAX_PRIORITY);
for(int i = 0; i < 5; i++)
new SimplePriorities(Thread.MIN_PRIORITY);
}
}

Result:
Thread[Thread-0,10,main]: 5

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Page 107

.
.
.

How to monitor a thread's status?

Solution:
Following example demonstrates how to monitor a thread's status by extending Thread class and using
currentThread.getName() method.
class MyThread extends Thread{
boolean waiting= true;
boolean ready= false;
MyThread() {
}
public void run() {
String thrdName = Thread.currentThread().getName();
System.out.println(thrdName + " starting.");
while(waiting)
System.out.println("waiting:"+waiting);
System.out.println("waiting...");
startWait();
try {
Thread.sleep(1000);
}
catch(Exception exc) {
System.out.println(thrdName + " interrupted.");
}
System.out.println(thrdName + " terminating.");
}
synchronized void startWait() {
try {
while(!ready) wait();
}
catch(InterruptedException exc) {
System.out.println("wait() interrupted");
}
}
synchronized void notice() {
ready = true;
notify();
}
}
public class Main {

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Page 108

throws Exception{
MyThread thrd = new MyThread();
thrd.setName("MyThread #1");
showThreadStatus(thrd);
thrd.start();
Thread.sleep(50);
thrd.waiting = false;
Thread.sleep(50);
thrd.notice();
Thread.sleep(50);
while(thrd.isAlive())
System.out.println("alive");
}
static void showThreadStatus(Thread thrd) {
System.out.println(thrd.getName()+"
Alive:="+thrd.isAlive()+"
State:=" + thrd.getState() );
}
}

Result:
main Alive=true State:=running

How to get the name of a running thread?

Solution:
Following example shows How to get the name of a running thread .
public class TwoThreadGetName extends Thread {
public void run() {
for (int i = 0; i < 10; i++) {
printMsg();
}
}
public void printMsg() {
String name = t.getName();
System.out.println("name=" + name);
}
TwoThreadGetName tt = new TwoThreadGetName();
tt.start();
for (int i = 0; i < 10; i++) {
tt.printMsg();
}
}
}

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Page 109

Result:
name=main
name=main
name=main
name=main
name=main
name=thread
name=thread
name=thread
name=thread

How to solve the producer consumer problem using thread?

Solution:
Following example demonstrates how to solve the producer consumer problem using thread.
public class ProducerConsumerTest {
CubbyHole c = new CubbyHole();
Producer p1 = new Producer(c, 1);
Consumer c1 = new Consumer(c, 1);
p1.start();
c1.start();
}
}
class CubbyHole {
private int contents;
private boolean available = false;
public synchronized int get() {
while (available == false) {
try {
wait();
}
}
}
available = false;
notifyAll();
return contents;
}
public synchronized void put(int value) {
while (available == true) {
try {
wait();
}
}
}
contents = value;
available = true;
notifyAll();
}
}

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Page 110

class Consumer extends Thread {
private CubbyHole cubbyhole;
private int number;
public Consumer(CubbyHole c, int number) {
cubbyhole = c;
this.number = number;
}
public void run() {
int value = 0;
for (int i = 0; i < 10; i++) {
value = cubbyhole.get();
System.out.println("Consumer #"
+ this.number
+ " got: " + value);
}
}
}
class Producer extends Thread {
private CubbyHole cubbyhole;
private int number;
public Producer(CubbyHole c, int number) {
cubbyhole = c;
this.number = number;
}
public void run() {
for (int i = 0; i < 10; i++) {
cubbyhole.put(i);
System.out.println("Producer #" + this.number
+ " put: " + i);
try {
sleep((int)(Math.random() * 100));
} catch (InterruptedException e) { }
}
}
}

Result:
Producer
Consumer
Producer
Consumer
Producer
Consumer
Producer
Consumer
Producer
Consumer
Producer
Consumer
Producer
Consumer
Producer
Consumer
Producer
Consumer
Producer

#1
#1
#1
#1
#1
#1
#1
#1
#1
#1
#1
#1
#1
#1
#1
#1
#1
#1
#1

put:
got:
put:
got:
put:
got:
put:
got:
put:
got:
put:
got:
put:
got:
put:
got:
put:
got:
put:

0
0
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9

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Page 111

Consumer #1 got: 9

How to set the priority of a thread?

Solution:
Following example how to set the priority of a thread with the help of.
public class Main {
throws Exception {
Thread thread1 = new Thread(new TestThread(1));
Thread thread2 = new Thread(new TestThread(2));
thread1.setPriority(Thread.MAX_PRIORITY);
thread2.setPriority(Thread.MIN_PRIORITY);
thread1.start();
thread2.start();
thread1.join();
thread2.join();
System.out.println("The priority has been set.");
}
}

Result:
The priority has been set.

How to stop a thread for a while?

Solution:
Following example demonstates how to stop a thread by creating an user defined method run() taking the help
of Timer classes' methods.
import java.util.Timer;
import java.util.TimerTask;
class CanStop extends Thread {
private volatile boolean stop = false;
private int counter = 0;
public void run() {
while (!stop && counter < 10000) {
System.out.println(counter++);
}
if (stop)
System.out.println("Detected stop");
}
public void requestStop() {
stop = true;

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Page 112

}
}
public class Stopping {
final CanStop stoppable = new CanStop();
stoppable.start();
new Timer(true).schedule(new TimerTask() {
public void run() {
System.out.println("Requesting stop");
stoppable.requestStop();
}
}, 350);
}
}

Result:
Detected stop

How to suspend a thread for a while?

Solution:
Following example shows how to suspend a thread for a while by creating sleepingThread() method.
public class SleepingThread extends Thread {
private int countDown = 5;
private static int threadCount = 0;
public SleepingThread() {
super("" + ++threadCount);
start();
}
return "#" + getName() + ": " + countDown;
}
public void run() {
while (true) {
System.out.println(this);
if (--countDown == 0)
return;
try {
sleep(100);
}
throw new RuntimeException(e);
}
}
}
for (int i = 0; i < 5; i++)
new SleepingThread().join();
System.out.println("The thread has been suspened.");
}
}

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Page 113

Result:
The thread has been suspened.

How to get the Id of the running thread?

Solution:
Following example demonstrates how to get the Id of a running thread using getThreadId() method.
public class Main extends Object implements Runnable {
private ThreadID var;
public Main(ThreadID v) {
this.var = v;
}
public void run() {
try {
print("var getThreadID =" + var.getThreadID());
Thread.sleep(2000);
print("var getThreadID =" + var.getThreadID());
} catch (InterruptedException x) {
}
}
private static void print(String msg) {
String name = Thread.currentThread().getName();
System.out.println(name + ": " + msg);
}
ThreadID tid = new ThreadID();
Main shared = new Main(tid);
try {
Thread threadA = new Thread(shared, "threadA");
threadA.start();
Thread.sleep(500);
Thread threadB = new Thread(shared, "threadB");
threadB.start();
Thread.sleep(500);
Thread threadC = new Thread(shared, "threadC");
threadC.start();
} catch (InterruptedException x) {
}
}
}
class ThreadID extends ThreadLocal {
private int nextID;

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Page 114

public ThreadID() {
nextID = 10001;
}
private synchronized Integer getNewID() {
Integer id = new Integer(nextID);
nextID++;
return id;
}
protected Object initialValue() {
print("in initialValue()");
return getNewID();
}
public int getThreadID() {
Integer id = (Integer) get();
return id.intValue();
}
private static void print(String msg) {
String name = Thread.currentThread().getName();
System.out.println(name + ": " + msg);
}
}

Result:
threadA:
threadA:
threadB:
threadB:
threadC:
threadC:
threadA:
threadB:
threadC:

in initialValue()
var getThreadID =10001
in initialValue()
in initialValue()

How to check priority level of a thread?

Solution:
Following example demonstrates how to check priority level of a thread using getPriority() method of a Thread.
public class Main extends Object {
private static Runnable makeRunnable() {
Runnable r = new Runnable() {
public void run() {
for (int i = 0; i < 5; i++) {
System.out.println("in run() - priority="
+ t.getPriority()+ ", name=" + t.getName());
try {
Thread.sleep(2000);

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}
catch (InterruptedException x) {
}
}
}
};
return r;
}
System.out.println("in main() - Thread.currentThread().
getPriority()=" + Thread.currentThread().getPriority());
System.out.println("in main() - Thread.currentThread()
.getName()="+ Thread.currentThread().getName());
Thread threadA = new Thread(makeRunnable(), "threadA");
threadA.start();
try {
Thread.sleep(3000);
}
}
System.out.println("in main() - threadA.getPriority()="
+ threadA.getPriority());
}
}

Result:
in
in
in
in
in
in
in
in

main() - Thread.currentThread().getPriority()=5
main() - Thread.currentThread().getName()=main
run() - priority=5, name=threadA
main() - threadA.getPriority()=5

How to display all running Thread?

Solution:
Following example demonstrates how to display names of all the running threads using getName() method.
public class Main extends Thread {
Main t1 = new Main();
t1.setName("thread1");
t1.start();
ThreadGroup currentGroup =
Thread.currentThread().getThreadGroup();
int noThreads = currentGroup.activeCount();
Thread[] lstThreads = new Thread[noThreads];
currentGroup.enumerate(lstThreads);
for (int i = 0; i < noThreads; i++)
System.out.println("Thread No:" + i + " = "
+ lstThreads[i].getName());

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Page 116

}
}

Result:
Thread No:0 = main
Thread No:1 = thread1

How to display thread status?

Solution:
Following example demonstrates how to display different status of thread using isAlive() & getStatus()
methods of Thread.
class MyThread extends Thread{
boolean waiting= true;
boolean ready= false;
MyThread() {
}
public void run() {
String thrdName = Thread.currentThread().getName();
System.out.println(thrdName + " starting.");
while(waiting)
System.out.println("waiting:"+waiting);
System.out.println("waiting...");
startWait();
try {
Thread.sleep(1000);
}
catch(Exception exc) {
System.out.println(thrdName + " interrupted.");
}
System.out.println(thrdName + " terminating.");
}
synchronized void startWait() {
try {
while(!ready) wait();
}
catch(InterruptedException exc) {
System.out.println("wait() interrupted");
}
}
synchronized void notice() {
ready = true;
notify();
}
}
public class Main {
throws Exception{
MyThread thrd = new MyThread();
thrd.setName("MyThread #1");

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thrd.start();
Thread.sleep(50);
thrd.waiting = false;
Thread.sleep(50);
thrd.notice();
Thread.sleep(50);
while(thrd.isAlive())
System.out.println("alive");
}
static void showThreadStatus(Thread thrd) {
System.out.println(thrd.getName()+" Alive:"
+thrd.isAlive()+" State:" + thrd.getState() );
}
}

Result:
MyThread #1 Alive:false State:NEW
MyThread #1 starting.
waiting:true
waiting:true
alive
alive
MyThread #1 terminating.
alive
MyThread #1 Alive:false State:TERMINATED

How to interrupt a running Thread?

Solution:
Following example demonstrates how to interrupt a running thread interrupt() method of thread and check if a
thread is interrupted using isInterrupted() method.
public class GeneralInterrupt extends Object
implements Runnable {
public void run() {
try {
System.out.println("in run() about to work2()");
work2();
System.out.println("in run() back from work2()");
}
System.out.println("in run() interrupted in work2()");
return;
}
System.out.println("in run() -

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doing stuff after nap");
System.out.println("in run() leaving normally");
}
public void work2() throws InterruptedException {
while (true) {
if (Thread.currentThread().isInterrupted()) {
System.out.println("C isInterrupted()="
+ Thread.currentThread().isInterrupted());
Thread.sleep(2000);
System.out.println("D isInterrupted()="
}
}
}
public void work() throws InterruptedException {
while (true) {
for (int i = 0; i < 100000; i++) {
int j = i * 2;
}
System.out.println("A isInterrupted()="
if (Thread.interrupted()) {
System.out.println("B isInterrupted()="
throw new InterruptedException();
}
}
}
GeneralInterrupt si = new GeneralInterrupt();
Thread t = new Thread(si);
t.start();
try {
Thread.sleep(2000);
}
}
System.out.println("in main() interrupting other thread");
t.interrupt();
System.out.println("in main() - leaving");
}
}

Result:
in run() - about to work2()
in main() - interrupting other thread
in main() - leaving
C isInterrupted()=true
in run() - interrupted in work2()

Java Applet - Programming Examples
Learn how to play with Applets in Java programming. Here are most commonly used examples:
1. How to create a basic Applet?

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2. How to create a banner using Applet?
3. How to display clock using Applet?
4. How to create different shapes using Applet?
5. How to fill colors in shapes using Applet?
6. How to goto a link using Applet?
7. How to create an event listener in Applet?
8. How to display image using Applet?
9. How to open a link in a new window using Applet?
10. How to play sound using Applet?
11. How to read a file using Applet?
12. How to write to a file using Applet?
13. How to use swing applet in JAVA?

How to create a basic Applet?

Solution:
Following example demonstrates how to create a basic Applet by extrnding Applet Class.You will need to
embed another HTML code to run this program.
import java.applet.*;
import java.awt.*;
public class Main extends Applet{
public void paint(Graphics g){
g.drawString("Welcome in Java Applet.",40,20);
}
}

Now compile the above code and call the generated class in your HTML code as follows:
<HTML>
<HEAD>
</HEAD>
<BODY>
<div >
<APPLET CODE="Main.class" WIDTH="800" HEIGHT="500">
</APPLET>
</div>
</BODY>
</HTML>

Result:
The above code sample will produce the following result in a java enabled web browser.
Welcome in Java Applet.

How to create a banner using Applet?

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Solution:
Following example demonstrates how to play a sound using an applet image using Thread class. It also uses
drawRect(), fillRect() , drawString() methods of Graphics class.
import java.awt.*;
public class SampleBanner extends Applet
implements Runnable{
String str = "This is a simple Banner ";
Thread t ;
boolean b;
public void init() {
setBackground(Color.gray);
setForeground(Color.yellow);
}
public void start() {
t = new Thread(this);
b = false;
t.start();
}
public void run () {
char ch;
for( ; ; ) {
try {
repaint();
Thread.sleep(250);
ch = str.charAt(0);
str = str.substring(1, str.length());
str = str + ch;
}
catch(InterruptedException e) {}
}
}
public void paint(Graphics g) {
g.drawRect(1,1,300,150);
g.setColor(Color.yellow);
g.fillRect(1,1,300,150);
g.setColor(Color.red);
g.drawString(str, 1, 150);
}
}

Result:
View in Browser.

How to display clock using Applet?

Solution:
Following example demonstrates how to display a clock using valueOf() mehtods of String Class. & using
Calender class to get the second, minutes & hours.

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import java.awt.*;
import java.awt.*;
import java.util.*;
public class ClockApplet extends Applet implements Runnable{
Thread t,t1;
public void start(){
t = new Thread(this);
t.start();
}
public void run(){
t1 = Thread.currentThread();
while(t1 == t){
repaint();
try{
t1.sleep(1000);
}
catch(InterruptedException e){}
}
}
Calendar cal = new GregorianCalendar();
String hour = String.valueOf(cal.get(Calendar.HOUR));
String minute = String.valueOf(cal.get(Calendar.MINUTE));
String second = String.valueOf(cal.get(Calendar.SECOND));
g.drawString(hour + ":" + minute + ":" + second, 20, 30);
}
}

Result:
View in Browser.

How to create different shapes using Applet?

Solution:
Following example demonstrates how to create an applet which will have a line, an Oval & a Rectangle using
drawLine(), drawOval(, drawRect() methods of Graphics clas.
import java.awt.*;
public class Shapes extends Applet{
int x=300,y=100,r=50;
g.drawLine(30,300,200,10);
g.drawOval(x-r,y-r,100,100);
g.drawRect(400,50,200,100);
}
}

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Result:
A line , Oval & a Rectangle will be drawn in the browser.

How to fill colors in shapes using Applet?

Solution:
Following example demonstrates how to create an applet which will have fill color in a rectangle using
setColor(), fillRect() methods of Graphics class to fill color in a Rectangle.
import java.awt.*;
public class fillColor extends Applet{
g.drawRect(300,150,200,100);
g.setColor(Color.yellow);
g.fillRect( 300,150, 200, 100 );
g.setColor(Color.magenta);
g.drawString("Rectangle",500,150);
}
}

Result:
A Rectangle with yellow color filled in it willl be drawn in the browser.

How to goto a link using Applet?

Solution:
Following example demonstrates how to go to a particular webpage from an applet using showDocument()
method of AppletContext class.
import
import
import
import

java.applet.*;
java.awt.*;
java.net.*;
java.awt.event.*;

public class tesURL extends Applet implements ActionListener{
public void init(){
String link = "yahoo";
Button b = new Button(link);
b.addActionListener(this);

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add(b);
}
public void actionPerformed(ActionEvent ae){
Button src = (Button)ae.getSource();
String link = "http://www."+src.getLabel()+".com";
try{
AppletContext a = getAppletContext();
URL u = new URL(link);
a.showDocument(u,"_self");
}
catch (MalformedURLException e){
System.out.println(e.getMessage());
}
}
}

Result:
View in Browser.

How to create an event listener in Applet?

Solution:
Following example demonstrates how to create a basic Applet having buttons to add & subtract two nos.
Methods usded here are addActionListener() to listen to an event(click on a button) & Button() construxtor to
create a button.
import java.awt.event.*;
import java.awt.*;
public class EventListeners extends Applet
implements ActionListener{
TextArea txtArea;
String Add, Subtract;
int i = 10, j = 20, sum =0,Sub=0;
public void init(){
txtArea = new TextArea(10,20);
txtArea.setEditable(false);
add(txtArea,"center");
Button b = new Button("Add");
Button c = new Button("Subtract");
b.addActionListener(this);
c.addActionListener(this);
add(b);
add(c);
}
public void actionPerformed(ActionEvent e){
sum = i + j;
txtArea.setText("");
txtArea.append("i = "+ i + "t" + "j = " + j + "n");
Button source = (Button)e.getSource();
if(source.getLabel() == "Add"){

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txtArea.append("Sum : " + sum + "n");
}
if(i >j){
Sub = i - j;
}
else{
Sub = j - i;
}
if(source.getLabel() == "Subtract"){
txtArea.append("Sub : " + Sub + "n");
}
}
}

Result:
View in Browser.

Java Simple GUI - Programming Examples
Learn how to play with Simple GUI in Java programming. Here are most commonly used examples:
1. How to display text in different fonts?
2. How to draw a line using GUI?
3. How to display a message in a new frame?
4. How to draw a polygon using GUI?
5. How to display string in a rectangle?
6. How to display different shapes using GUI?
7. How to draw a solid rectange using GUI?
8. How to create a transparent cursor?
9. How to check whether antialiasing is enabled or not?
10. How to display colours in a frame?
11. How to display a pie chart using a frame?
12. How to draw text using GUI?

How to display text in different fonts?

Solution:
Following example demonstrates how to display text in different fonts using setFont() method of Font class.
import java.awt.*;
import java.awt.event.*
import javax.swing.*
public class Main extends JPanel {
String[] type = { "Serif","SansSerif"};

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int[] styles = { Font.PLAIN, Font.ITALIC, Font.BOLD,
Font.ITALIC + Font.BOLD };
String[] stylenames =
{ "Plain", "Italic", "Bold", "Bold & Italic" };
for (int f = 0; f < type.length; f++) {
for (int s = 0; s < styles.length; s++) {
Font font = new Font(type[f], styles[s], 18);
g.setFont(font);
String name = type[f] + " " + stylenames[s];
g.drawString(name, 20, (f * 4 + s + 1) * 20);
}
}
}
JFrame f = new JFrame();
f.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
}
);
f.setContentPane(new Main());
f.setSize(400,400);
f.setVisible(true);
}
}

Result:
Different font names are displayed in a frame.

How to draw a line using GUI?

Solution:
Following example demonstrates how to draw a line using draw() method of Graphics2D class with Line2D
object as an argument.
import
import
import
import
import

java.awt.*;
java.awt.event.*;
java.awt.geom.Line2D;
javax.swing.JApplet;
javax.swing.JFrame;

public class Main extends JApplet {
public void init() {
setBackground(Color.white);
setForeground(Color.white);
}
Graphics2D g2 = (Graphics2D) g;
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,

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RenderingHints.VALUE_ANTIALIAS_ON);
g2.setPaint(Color.gray);
int x = 5;
int y = 7;
g2.draw(new Line2D.Double(x, y, 200, 200));
g2.drawString("Line", x, 250);
}
public static void main(String s[]) {
JFrame f = new JFrame("Line");
System.exit(0);
}
});
JApplet applet = new Main();
f.getContentPane().add("Center", applet);
applet.init();
f.pack();
f.setSize(new Dimension(300, 300));
f.setVisible(true);
}
}

Result:
Line is displayed in a frame.

How to display a message in a new frame?

Solution:
Following example demonstrates how to display message in a new frame by creating a frame using JFrame() &
using JFrames getContentPanel(), setSize() & setVisible() methods to display this frame.
import
import
import
import
import

java.awt.*;
java.awt.font.FontRenderContext;
java.awt.geom.Rectangle2D;
javax.swing.JFrame;
javax.swing.JPanel;

g2.setFont(new Font("Serif", Font.PLAIN, 48));
paintHorizontallyCenteredText(g2, "Java Source", 200, 75);
paintHorizontallyCenteredText(g2, "and", 200, 125);
paintHorizontallyCenteredText(g2, "Support", 200, 175);
}
protected void paintHorizontallyCenteredText(Graphics2D g2,
String s, float centerX, float baselineY) {
FontRenderContext frc = g2.getFontRenderContext();
Rectangle2D bounds = g2.getFont().getStringBounds(s, frc);

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float width = (float) bounds.getWidth();
g2.drawString(s, centerX - width / 2, baselineY);
}
f.getContentPane().add(new Main());
f.setSize(450, 350);
f.setVisible(true);
}
}

Result:
JAVA and J2EE displayed in a new Frame.

How to draw a polygon using GUI?

Solution:
Following example demonstrates how to draw a polygon by creating Polygon() object. addPoint() &
drawPolygon() method is used to draw the Polygon.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public void paintComponent(Graphics g) {
super.paintComponent(g);
Polygon p = new Polygon();
for (int i = 0; i < 5; i++)
p.addPoint((int)
(100 + 50 * Math.cos(i * 2 * Math.PI / 5)),
(int) (100 + 50 * Math.sin(i * 2 * Math.PI / 5)));
g.drawPolygon(p);
}
JFrame frame = new JFrame();
frame.setTitle("Polygon");
frame.setSize(350, 250);
frame.addWindowListener(new WindowAdapter() {
System.exit(0);
}
});
Container contentPane = frame.getContentPane();
contentPane.add(new Main());
frame.setVisible(true);
}
}

Result:

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Polygon is displayed in a frame.

How to display string in a rectangle?

Solution:
Following example demonstrates how to display each character in a rectangle by drawing a rectangle around
each character using drawRect() method.
import java.awt.*;
import javax.swing.*
g.setFont(new Font("",0,100));
FontMetrics fm = getFontMetrics(new Font("",0,100));
String s = "message";
int x = 5;
int y = 5;
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
int h = fm.getHeight();
int w = fm.charWidth(c);
g.drawRect(x, y, w, h);
g.drawString(String.valueOf(c), x, y + h);
x = x + w;
}
}
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setContentPane(new Main());
}
}

Result:
Each character is displayed in a rectangle.

How to display different shapes using GUI?

Solution:
Following example demonstrates how to display different shapes using Arc2D, Ellipse2D, Rectangle2D,
RoundRectangle2D classes.
import java.awt.Shape;

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import java.awt.geom.*;
public class Main {
int x1 = 1, x2 = 2, w = 3, h = 4,
x = 5, y = 6,
y1 = 1, y2 = 2, start = 3;
Shape line = new Line2D.Float(x1, y1, x2, y2);
Shape arc = new Arc2D.Float(x, y, w, h, start, 1, 1);
Shape oval = new Ellipse2D.Float(x, y, w, h);
Shape rectangle = new Rectangle2D.Float(x, y, w, h);
Shape roundRectangle = new RoundRectangle2D.Float
(x, y, w, h, 1, 2);
System.out.println("Different shapes are created:");
}
}

Result:
Different shapes are created.

How to draw a solid rectangle using GUI?

Solution:
Following example demonstrates how to display a solid rectangle using fillRect() method of Graphics class.
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
f.add(new Main());
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
}
g.fillRect (5, 15, 50, 75);
}
}

Result:
Solid rectangle is created.

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How to create a transparent cursor?

Solution:
Following example demonstrates how to create a transparent cursor by using createCustomCursor() method
with "invisiblecursor" as an argument.
import java.awt.*;
import java.awt.image.MemoryImageSource;
public class Main {
int[] pixels = new int[16 * 16];
Image image = Toolkit.getDefaultToolkit().createImage(
new MemoryImageSource(16, 16, pixels, 0, 16));
Cursor transparentCursor = Toolkit.getDefaultToolkit().
createCustomCursor(image, new Point(0, 0),
"invisibleCursor");
System.out.println("Transparent Cursor created.");
}
}

Result:
Transparent Cursor created.

How to check whether antialiasing is enabled or not?

Solution:
Following example demonstrates how to check if antialiasing is turned on or not using RenderingHints Class.
import
import
import
import
import

java.awt.Graphics;
java.awt.Graphics2D;
java.awt.RenderingHints;
javax.swing.JComponent;
javax.swing.JFrame;

public class Main {
frame.add(new MyComponent());
}
}
class MyComponent extends JComponent {
RenderingHints rh = g2d.getRenderingHints();

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boolean bl = rh.containsValue
(RenderingHints.VALUE_ANTIALIAS_ON);
System.out.println(bl);
g2.setRenderingHint(RenderingHints.
KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
}
}

Result:
False
False
False

How to display colours in a frame?

Solution:
Following example displays how to a display all the colors in a frame using setRGB method of image class.
import
import
import
import
import
import

java.awt.Graphics;
java.awt.event.WindowAdapter;
java.awt.event.WindowEvent;
java.awt.image.BufferedImage;
javax.swing.JComponent;
javax.swing.JFrame;

public class Main extends JComponent {
BufferedImage image;
public void initialize() {
int width = getSize().width;
int height = getSize().height;
int[] data = new int[width * height];
int index = 0;
for (int i = 0; i < height; i++) {
int red = (i * 255) / (height - 1);
for (int j = 0; j < width; j++) {
int green = (j * 255) / (width - 1);
int blue = 128;
data[index++] = (red < < 16) | (green < < 8) | blue;
}
}
image = new BufferedImage
(width, height, BufferedImage.TYPE_INT_RGB);
image.setRGB(0, 0, width, height, data, 0, width);
}
if (image == null)
initialize();
g.drawImage(image, 0, 0, this);
}
JFrame f = new JFrame("Display Colours");

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f.setLocation(100, 100);
System.exit(0);
}
});
f.setVisible(true);
}
}

Result:
Displays all the colours in a frame.

How to display a pie chart using a frame?

Solution:
Following example displays how to a display a piechart by making Slices class & creating arc depending on the
slices.
import
import
import
import

java.awt.Color;
java.awt.Graphics;
java.awt.Rectangle;

import javax.swing.JComponent;
class Slice {
double value;
Color color;
public Slice(double value, Color color) {
this.value = value;
this.color = color;
}
}
class MyComponent extends JComponent {
Slice[] slices = { new Slice(5, Color.black),
new Slice(33, Color.green),
new Slice(20, Color.yellow), new Slice(15, Color.red) };
MyComponent() {}
drawPie((Graphics2D) g, getBounds(), slices);
}
void drawPie(Graphics2D g, Rectangle area, Slice[] slices) {
double total = 0.0D;
for (int i = 0; i < slices.length; i++) {
total += slices[i].value;
}
double curValue = 0.0D;
int startAngle = 0;
for (int i = 0; i < slices.length; i++) {
startAngle = (int) (curValue * 360 / total);

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int arcAngle = (int) (slices[i].value * 360 / total);
g.setColor(slices[i].color);
g.fillArc(area.x, area.y, area.width, area.height,
startAngle, arcAngle);
curValue += slices[i].value;
}
}
}
public class Main {
frame.getContentPane().add(new MyComponent());
}
}

Result:
Displays a piechart in a frame.

How to draw text using GUI?

Solution:
Following example demonstrates how to draw text drawString(), setFont() methods of Graphics class.
import
import
import
import

java.awt.Font;
java.awt.Graphics;
java.awt.RenderingHints;

import javax.swing.JPanel;
public class Main extends JPanel{
Graphics2D g2 = (Graphics2D)g;
Font font = new Font("Serif", Font.PLAIN, 96);
g2.setFont(font);
g2.drawString("Text", 40, 120);
}
f.setVisible(true);
}
}

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Result:
Text is displayed in a frame.

Java JDBC - Programming Examples
Learn how to use JDBC in Java programming. Here are most commonly used examples:
1. How to establishing a connection with Database?
2. How to Create, edit & alter table using Java?
3. How to display contents of table ?
4. How to update, edit & delete rows ?
5. How to search in the database using java commands?
6. How to sort elements of a column using java commands?
7. How to combine data from more than one tables?
8. How to use commit statement in Java?
9. How to us prepared statement in Java?
10. How to set & rollback to a savepoint ?
11. How to execute a batch of SQL statements using java?
12. How to use different row methods in java?
13. How to use different column methods in java?

How to connect to a database using JDBC? Assume that database name is testDb and it has table named
employee which has 2 records.

Solution:
Following example uses getConnection, createStatement & executeQuery methods to connect to a database &
execute queries.
import java.sql.*;
public class jdbcConn {
try {
Class.forName("org.apache.derby.jdbc.ClientDriver");
}
catch(ClassNotFoundException e) {
System.out.println("Class not found "+ e);
}
System.out.println("JDBC Class found");
int no_of_rows = 0;
try {
Connection con = DriverManager.getConnection
("jdbc:derby://localhost:1527/testDb","username",
"password");

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Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery
("SELECT * FROM employee");
while (rs.next()) {
no_of_rows++;
}
System.out.println("There are "+ no_of_rows
+ " record in the table");
}
catch(SQLException e){
System.out.println("SQL exception occured" + e);
}
}
}

Result:
The above code sample will produce the following result.The result may vary. You will get ClassNotfound
exception if your JDBC driver is not installed properly.
JDBC Class found
There are 2 record in the table

How to edit(Add or update) columns of a Table and how to delete a table?

Solution:
Following example uses create, alter & drop SQL commands to create, edit or delete table
import java.sql.*;
public static void main(String[] args) throws Exception{
"password");
String query ="CREATE TABLE employees
(id INTEGER PRIMARY KEY,
first_name CHAR(50),last_name CHAR(75))";
stmt.execute(query);
System.out.println("Employee table created");
String query1 = "aLTER TABLE employees ADD
address CHAR(100) ";
String query2 = "ALTER TABLE employees DROP
COLUMN last_name";
stmt.execute(query1);
System.out.println("Address column added to the table
& last_name column removed from the table");
String query3 = "drop table employees";
System.out.println("Employees table removed");
}
}

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Result:
Employee table created
Address column added to the table & last_name
column removed from the table
Employees table removed from the database

How to retrieve contents of a table using JDBC connection?

Solution:
Following example uses getString,getInt & executeQuery methods to fetch & display the contents of the table.
import java.sql.*;
public class jdbcResultSet {
try {
}
}
try {
"password");
ResultSet rs = stmt.executeQuery
("SELECT * FROM employee");
System.out.println("id name
job");
while (rs.next()) {
int id = rs.getInt("id");
String name = rs.getString("name");
String job = rs.getString("job");
System.out.println(id+"
"+name+"
"+job);
}
}
}
}
}

Result:
id
1
2

name
alok
ravi

job
trainee
trainee

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How to update(delete, insert or update) contents of a table using JDBC connection?

Solution:
Following method uses update, delete & insert SQL commands to edit or delete row contents.
import java.sql.*;
public class updateTable {
try {
}
}
try {
"password");
String query1="update emp set name='ravi' where id=2";
String query2 = "delete from emp where id=1";
String query3 = "insert into emp values
(1,'ronak','manager')";
ResultSet rs = stmt.executeQuery("SELECT * FROM emp");
System.out.println("id name
job");
while (rs.next()) {
System.out.println(id+"
"+name+"
"+job);
}
}
}
}
}

Result:
id
2
1

name
ravi
ronak

job
trainee
manager

How to Search contents of a table?

Saikat Banerjee

Page 138

Solution:
Following method uses where & like sql Commands to search through the database.
import java.sql.*;
"password");
String query[] ={"SELECT * FROM emp where id=1",
"select name from emp where name like 'ravi_'",
"select name from emp where name like 'ravi%'"};
for(String q : query){
ResultSet rs = stmt.executeQuery(q);
System.out.println("Names for query "+q+" are");
while (rs.next()) {
System.out.print(name+" ");
}
}
}
}

Result:
Names
ravi
Names
ravi2
Names
ravi

for query SELECT * FROM emp where id=1 are
for query select name from emp where name like 'ravi_' are
ravi3
for query select name from emp where name like 'ravi%' are
ravi2 ravi3 ravi123 ravi222

How to sort contents of a table?

Solution:
Following example uses Order by SQL command to sort the table.
import java.sql.*;
("jdbc:derby://localhost:1527/testDb","name","pass");

Saikat Banerjee

Page 139

String query = "select * from emp order by name";
String query1="select * from emp order by name, job";
ResultSet rs = stmt.executeQuery(query);
System.out.println("Table contents sorted by Name");
System.out.println("Id Name
Job");
while (rs.next()) {
System.out.println(id + " " + name+"
"+job);
}
rs = stmt.executeQuery(query1);
System.out.println("Table contents after sorted
by Name & job");
System.out.println("Id Name
Job");
while (rs.next()) {
System.out.println(id + " " + name+"
"+job);
}
}
}

Result:
Table contents after sorting by Name
Id Name
Job
1 ravi
trainee
5 ravi
MD
4 ravi
CEO
2 ravindra
CEO
2 ravish
trainee
Table contents after sorting by Name & job
Id Name
Job
4 ravi
CEO
5 ravi
MD
1 ravi
trainee
2 ravindra
CEO
2 ravish
trainee

How to join contents of more than one table & display?

Solution:
Following example uses inner join sql command to combine data from two tables. To display the contents of
the table getString() method of resultset is used.
import java.sql.*;

Saikat Banerjee

Page 140

"password");
String query ="SELECT fname,lname,isbn from author
inner join books on author.AUTHORID = books.AUTHORID";
ResultSet rs = stmt.executeQuery(query);
System.out.println("Fname Lname
ISBN");
while (rs.next()) {
String fname = rs.getString("fname");
String lname = rs.getString("lname");
int isbn = rs.getInt("isbn");
System.out.println(fname + " " + lname+"
"+isbn);
}
}
}

Result:
Fname Lname
ISBN
john grisham
123
jeffry archer
113
jeffry archer
112
jeffry archer
122

Java Regular Expression - Programming Examples
Learn how to use regular expression in Java programming. Here are most commonly used examples:
1. How to reset the pattern of a regular expression?
2. How to match duplicate words in a regular expression?
3. How to find every occurance of a word?
4. How to know the last index of a perticular word in a string?
5. How to print all the strings that match a given pattern from a file?
6. How to remove the white spaces?
7. How to match phone numbers in a list to a certain pattern?
8. How to count a group of words in a string?
9. How to search a perticular word in a string?
10. How to split a regular expression?
11. How to count replace first occourance of a String?
12. How to check check whether date is in proper format or not?
13. How to validate an email address format?
14. How to replace all occurings of a string?
15. How to make first character of each word in Uppercase?

How to reset the pattern of a regular expression?

Saikat Banerjee

Page 141

Solution:
Following example demonstrates how to reset the pattern of a regular expression by using Pattern.compile() of
Pattern class and m.find() method of Matcher class.
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Resetting {
throws Exception {
Matcher m = Pattern.compile("[frb][aiu][gx]").
matcher("fix the rug with bags");
while (m.find())
System.out.println(m.group());
m.reset("fix the rig with rags");
while (m.find())
System.out.println(m.group());
}
}

Result:
fix
rug
bag
fix
rig
rag

How to match duplicate words in a regular expression?

Solution:
Following example shows how to search duplicate words in a regular expression by using p.matcher() method
and m.group() method of regex.Matcher class.
public class Main {
throws Exception {
String duplicatePattern = "b(w+) 1b";
Pattern p = Pattern.compile(duplicatePattern);
int matches = 0;
String phrase = " this is a test ";
Matcher m = p.matcher(phrase);
String val = null;
while (m.find()) {
val = ":" + m.group() + ":";
matches++;
}

Saikat Banerjee

Page 142

if(val>0)
System.out.println("The string
has matched with the pattern.");
else
System.out.println("The string
has not matched with the pattern.");
}
}

Result:
The string has matched with the pattern.

How to find every occurance of a word?

Solution:
Following example demonstrates how to find every occurance of a word with the help of Pattern.compile()
method and m.group() method.
public class Main {
throws Exception {
String candidate = "this is a test, A TEST.";
String regex = "baw*b";
Pattern p = Pattern.compile(regex);
Matcher m = p.matcher(candidate);
String val = null;
System.out.println("INPUT: " + candidate);
System.out.println("REGEX: " + regex + "rn");
while (m.find()) {
val = m.group();
System.out.println("MATCH: " + val);
}
if (val == null) {
System.out.println("NO MATCHES: ");
}
}
}

Result:
INPUT:
REGEX:
MATCH:
MATCH:

this is a test ,A TEST.
baw*b
a test
A TEST

Saikat Banerjee

Page 143

How to know the last index of a perticular word in a string?

Solution:
Following example demonstrates how to know the last index of a perticular word in a string by using
Patter.compile() method of Pattern class and matchet.find() method of Matcher class.
public class Main {
String candidateString = "This is a Java example.
This is another Java example.";
Pattern p = Pattern.compile("Java");
Matcher matcher = p.matcher(candidateString);
matcher.find();
int nextIndex = matcher.end();
System.out.print("The last index of Java is:");
System.out.println(nextIndex);
}
}

Result:
The last index of Java is: 42

How to print all the strings that match a given pattern from a file?

Solution:
Following example shows how to print all the strings that match a given pattern from a file with the help of
Patternname.matcher() method of Util.regex class.
import java.util.regex.*;
import java.io.*;
public class ReaderIter {
Pattern patt = Pattern.compile("[A-Za-z][a-z]+");
BufferedReader r = new BufferedReader
(new FileReader("ReaderIter.java"));
String line;
while ((line = r.readLine()) != null) {
Matcher m = patt.matcher(line);
while (m.find()) {
System.out.println(m.group(0));
int start = m.start(0);
int end = m.end(0);

Saikat Banerjee

Page 144

Use CharacterIterator.substring(offset, end);
System.out.println(line.substring(start, end));
}
}
}
}

Result:
Ian
Darwin
http
www
darwinsys
com
All
rights
reserved
Software
written
by
Ian
Darwin
and
others

How to remove the white spaces?

Solution:
Following example demonstrates how to remove the white spaces with the help matcher.replaceAll(stringname)
method of Util.regex.Pattern class.
public class Main {
throws Exception {
String ExString = "This is a Java program.
This is another Java Program.";
String result=removeDuplicateWhitespace(ExString);
System.out.println(result);
}
public static CharSequence
removeDuplicateWhitespace(CharSequence inputStr) {
String patternStr = "s+";
String replaceStr = " ";
Pattern pattern = Pattern.compile(patternStr);
Matcher matcher = pattern.matcher(inputStr);
return matcher.replaceAll(replaceStr);
}
}

Saikat Banerjee

Page 145

Result:
ThisisaJavaprogram.ThisisanotherJavaprogram.

How to match phone numbers in a list?

Solution:
Following example shows how to match phone numbers in a list to a perticlar pattern by using
phone.matches(phoneNumberPattern) method .
public class MatchPhoneNumber {
isPhoneValid("1-999-585-4009");
isPhoneValid("999-585-4009");
isPhoneValid("1-585-4009");
isPhoneValid("585-4009");
isPhoneValid("1.999-585-4009");
isPhoneValid("999 585-4009");
isPhoneValid("1 585 4009");
isPhoneValid("111-Java2s");
}
public static boolean isPhoneValid(String phone) {
boolean retval = false;
String phoneNumberPattern =
"(d-)?(d{3}-)?d{3}-d{4}";
retval = phone.matches(phoneNumberPattern);
String msg = "NO MATCH: pattern:" + phone
+ "rn regex: " + phoneNumberPattern;
if (retval) {
msg = " MATCH: pattern:" + phone
+ "rn regex: " + phoneNumberPattern;
}
System.out.println(msg + "rn");
return retval;
}
}

Result:
MATCH: pattern:1-999-585-4009
regex: (d-)?(d{3}-)?d{3}-d{4}
MATCH: pattern:999-585-4009
regex: (d-)?(d{3}-)?d{3}-d{4}
MATCH: pattern:1-585-4009
regex: (d-)?(d{3}-)?d{3}-d{4}
NOMATCH: pattern:1.999-585-4009
regex: (d-)?(d{3}-)?d{3}-d{4}
NOMATCH: pattern:999 585-4009
regex: (d-)?(d{3}-)?d{3}-d{4}
NOMATCH: pattern:1 585 4009

Saikat Banerjee

Page 146

regex: (d-)?(d{3}-)?d{3}-d{4}
NOMATCH: pattern:111-Java2s
regex: (d-)?(d{3}-)?d{3}-d{4}

How to count a group of words in a string?

Solution:
Following example demonstrates how to count a group of words in a string with the help of
matcher.groupCount() method of regex.Matcher class.
public class MatcherGroupCountExample {
Pattern p = Pattern.compile("J(ava)");
String candidateString = "This is Java.
This is a Java example.";
int numberOfGroups = matcher.groupCount();
System.out.println("numberOfGroups =" + numberOfGroups);
}
}

Result:
numberOfGroups =3

How to search a perticular word in a string?

Solution:
Following example demonstrates how to search a perticular word in a string with the help of matcher.start()
method of regex.Matcher class.
public class Main {
Pattern p = Pattern.compile("j(ava)");
String candidateString = "This is a java program.
This is another java program.";
int nextIndex = matcher.start(1);
System.out.println(candidateString);
System.out.println("The index for java is:"
+ nextIndex);

Saikat Banerjee

Page 147

}
}

Result:
This is a java program. This is another java program.
The index for java is: 11

How to split a regular expression?

Solution:
Following example demonstrates how to split a regular expression by using Pattern.compile() method and
patternname.split() method of regex.Pattern class.
public class PatternSplitExample {
Pattern p = Pattern.compile(" ");
String tmp = "this is the Java example";
String[] tokens = p.split(tmp);
for (int i = 0; i < tokens.length; i++) {
System.out.println(tokens[i]);
}
}
}

Result:
this
is
the
Java
example

How to count replace first occourance of a String?

Solution:
Following example demonstrates how to replace first occourance of a String in a String using replaceFirst()
method of a Matcher class.

Saikat Banerjee

Page 148

public class Main {
Pattern p = Pattern.compile("hello");
String instring = "hello hello hello.";
System.out.println("initial String: "+ instring);
Matcher m = p.matcher(instring);
String tmp = m.replaceFirst("Java");
System.out.println("String after replacing 1st Match: "
+tmp);
}
}

Result:
initial String: hello hello hello.
String after replacing 1st Match: Java hello hello.

How to check check whether date is in proper format or not?

Solution:
Following example demonstrates how to check whether the date is in a proper format or not using matches
method of String class.
public class Main {
boolean isDate = false;
String date1 = "8-05-1988";
String date2 = "08/04/1987" ;
String datePattern = "d{1,2}-d{1,2}-d{4}";
isDate = date1.matches(datePattern);
System.out.println("Date :"+ date1+": matches with
the this date Pattern:"+datePattern+"Ans:"+isDate);
isDate = date2.matches(datePattern);
System.out.println("Date :"+ date2+": matches with
the this date Pattern:"+datePattern+"Ans:"+isDate);
}
}

Result:
Date :8-05-1988: matches with the this date Pattern:
d{1,2}-d{1,2}-d{4}Ans:true
Date :08/04/1987: matches with the this date Pattern:
d{1,2}-d{1,2}-d{4}Ans:false

Saikat Banerjee

Page 149

How to validate an email address format?

Solution:
Following example demonstrates how to validate e-mail address using matches() method of String class.
public class Main {
String EMAIL_REGEX = "^[w-_.+]*[w-_.]
@([w]+.)+[w]+[w]$";
String email1 = "user@domain.com";
Boolean b = email1.matches(EMAIL_REGEX);
System.out.println("is e-mail: "+email1+" :Valid = " + b);
String email2 = "user^domain.co.in";
b = email2.matches(EMAIL_REGEX);
System.out.println("is e-mail: "+email2
+" :Valid = " + b);
}
}

Result:
is e-mail: user@domain.com :Valid = true
is e-mail: user^domain.co.in :Valid = false

How to replace all occurings of a string?

Solution:
Following example demonstrates how to replace all occouranc of a String in a String using replaceAll() method
of Matcher class.
public class Main {
Pattern p = Pattern.compile("hello");
String instring = "hello hello hello.";
System.out.println("initial String: "+ instring);
Matcher m = p.matcher(instring);
String tmp = m.replaceAll("Java");
System.out.println("String after replacing 1st Match: "
+tmp);
}
}

Saikat Banerjee

Page 150

Result:
initial String: hello hello hello.
String after replacing 1st Match: Java Java Java.

How to make first character of each word in Uppercase?

Solution:
Following example demonstrates how to convert first letter of each word in a string into an uppercase letter
Using toUpperCase(), appendTail() methods.
public class Main {
String str = "this is a java test";
StringBuffer stringbf = new StringBuffer();
Matcher m = Pattern.compile("([a-z])([a-z]*)",
Pattern.CASE_INSENSITIVE).matcher(str);
while (m.find()) {
m.appendReplacement(stringbf,
m.group(1).toUpperCase() + m.group(2).toLowerCase());
}
System.out.println(m.appendTail(stringbf).toString());
}
}

Result:
this is a java test
This Is A Java Test

Saikat Banerjee

Page 151

Java programming-examples

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