Java Programming - 03 java control flow

Module 03 – Control Flow and
Exception Handling
Danairat T.
Line ID: Danairat
FB: Danairat Thanabodithammachari
+668-1559-1446

Fundamental Java Programming
The Course Outline
Module 01 – Introduction to Java
Module 02 – Basic Java Programming
Module 03 – Control Flow and Exception Handling
Module 04 – Object Oriented in Java
Module 05 – Java Package and Access Control
Module 06 – Java File IO
Module 07 – Java Networking
Module 08 – Java Threading

Module 03 – Control Flow and Exception Handling
• The if-then and if-then-else Statements
• The switch Statement
• The while and do-while Statements
• The for Statement
• Branching Statements
• Exception Handling

Control Flow Statements
The statements inside your source files are generally
executed from top to bottom, in the order that they appear.
Control flow statements break up the flow of execution by
employing decision making, looping, and branching,
enabling your program to conditionally execute particular
blocks of code.

The if-then Statement
void applyBrakes(){
if (isMoving){ // the "if" clause: bicycle must be moving
currentSpeed--; // the "then" clause: decrease current speed
}
}

The if-then-else Statement
void applyBrakes(){
if (isMoving) {
currentSpeed--;
} else {
System.err.println("The bicycle has already stopped!");
}
}

LAB - IfElseDemo
class IfElseDemo {
public static void main(String[] args) {
int testscore = 76;
char grade;
if (testscore >= 90) {
grade = 'A';
} else if (testscore >= 80) {
grade = 'B';
grade = 'C';
grade = 'D';
} else {
grade = 'F';
}
System.out.println("Grade = " + grade);
}
}

LAB - SwitchDemo
A statement in the switch block can be labeled with one or more case or default labels with
break label.
public class SwitchDemo {
int month = 8;
String monthString;
switch (month) {
case 1: monthString = "January"; break;
case 2: monthString = "February"; break;
case 3: monthString = "March"; break;
case 4: monthString = "April"; break;
case 5: monthString = "May"; break;
case 6: monthString = "June"; break;
case 7: monthString = "July"; break;
case 8: monthString = "August"; break;
case 9: monthString = "September"; break;
case 10: monthString = "October"; break;
case 11: monthString = "November"; break;
case 12: monthString = "December"; break;
default: monthString = "Invalid month"; break;
}
System.out.println(monthString);
}
}

LAB - SwitchDemoFallThrough
A statement in the switch block can be labeled with one or more case or default labels with
break label.
public class SwitchDemoFallThrough {
public static void main(String args[]) {
java.util.ArrayList<String> futureMonths = new
java.util.ArrayList<String>();
int month = 8;
switch (month) {
case 1: futureMonths.add("January");
case 2: futureMonths.add("February");
case 3: futureMonths.add("March");
case 4: futureMonths.add("April");
case 5: futureMonths.add("May");
case 6: futureMonths.add("June");
case 7: futureMonths.add("July");
case 8: futureMonths.add("August");
case 9: futureMonths.add("September");
case 10: futureMonths.add("October");
case 11: futureMonths.add("November");
case 12: futureMonths.add("December"); break;
default: break;
}
if (futureMonths.isEmpty()) {
System.out.println("Invalid month number");
} else {
for (String monthName : futureMonths) {
System.out.println(monthName);
}
}
}
}
August
September
October
November
December

LAB - SwitchDemo2
class SwitchDemo2 {
int month = 2;
int year = 2000;
int numDays = 0;
switch (month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
numDays = 31;
break;
case 4:
case 6:
case 9:
case 11:
numDays = 30;
break;
case 2:
if ( ((year % 4 == 0) && !(year % 100 == 0))
|| (year % 400 == 0) )
numDays = 29;
else
numDays = 28;
break;
default:
System.out.println("Invalid month.");
break;
}
System.out.println("Number of Days = " + numDays);
}
}
Number of Days = 29

LAB - StringSwitchDemo
public class StringSwitchDemo {
public static int getMonthNumber(String month) {
int monthNumber = 0;
if (month == null) { return monthNumber; }
switch (month.toLowerCase()) {
case "january": monthNumber = 1; break;
case "february": monthNumber = 2; break;
case "march": monthNumber = 3; break;
case "april": monthNumber = 4; break;
case "may": monthNumber = 5; break;
case "june": monthNumber = 6; break;
case "july": monthNumber = 7; break;
case "august": monthNumber = 8; break;
case "september": monthNumber = 9; break;
case "october": monthNumber = 10; break;
case "november": monthNumber = 11; break;
case "december": monthNumber = 12; break;
default: monthNumber = 0; break;
}
return monthNumber;
}
String month = "August";
int returnedMonthNumber =
StringSwitchDemo.getMonthNumber(month);
if (returnedMonthNumber == 0) {
System.out.println("Invalid month");
} else {
System.out.println(returnedMonthNumber);
}
}
}
The output from this code is 8.

The while and do-while Statements
The while statement evaluates expression, which must return a
boolean value. If the expression evaluates to true, the while
statement executes the statement(s) in the while block. The while
statement continues testing the expression and executing its block
until the expression evaluates to false.
class WhileDemo {
public static void main(String[] args){
int count = 1;
while (count < 11) {
System.out.println("Count is: " + count);
count++;
}
}
}

LAB – Do-While
class DoWhileDemo {
int count = 1;
do {
System.out.println("Count is: " + count);
count++;
} while (count <= 11);
}
}

The for Statement
The for statement provides a compact way to iterate over a
range of values.
class ForDemo {
for(int i=1; i<11; i++){
System.out.println("Count is: " + i);
}
}
}
Count is: 1
Count is: 2
Count is: 3
Count is: 4
Count is: 5
Count is: 6
Count is: 7
Count is: 8
Count is: 9
Count is: 10

LAB - ForEachDemo
class ForEachDemo {
int[] numbers = {1,2,3,4,5,6,7,8,9,10};
for (int item : numbers) {
System.out.println("Count is: " + item);
}
}
}
Count is: 1
Count is: 2
Count is: 3
Count is: 4
Count is: 5
Count is: 6
Count is: 7
Count is: 8
Count is: 9
Count is: 10

The break Statement
The break statement has two forms: labeled and unlabeled.
You saw the unlabeled form in the previous discussion of
the switch statement. You can also use an unlabeled break
to terminate a for, while, or do-while loop
class BreakDemo {
int[] arrayOfInts = { 32, 87, 3, 589, 12, 1076,
2000, 8, 622, 127 };
int searchfor = 12;
int i;
boolean foundIt = false;
for (i = 0; i < arrayOfInts.length; i++) {
if (arrayOfInts[i] == searchfor) {
foundIt = true;
break;
}
}
if (foundIt) {
System.out.println("Found " + searchfor
+ " at index " + i);
} else {
System.out.println(searchfor
+ " not in the array");
}
}
} Found 12 at index 4

LAB - BreakWithLabelDemo
The following program, BreakWithLabelDemo, is similar to the previous program, but uses nested for loops to
search for a value in a two-dimensional array. When the value is found, a labeled break terminates the outer for loop
(labeled "search"):
Found 12 at 1, 0
class BreakWithLabelDemo {
int[][] arrayOfInts = { { 32, 87, 3, 589 },
{ 12, 1076, 2000, 8 },
{ 622, 127, 77, 955 }
};
int searchfor = 12;
int i;
int j = 0;
search:
for (i = 0; i < arrayOfInts.length; i++) {
for (j = 0; j < arrayOfInts[i].length; j++) {
if (arrayOfInts[i][j] == searchfor) {
foundIt = true;
break search;
}
}
}
if (foundIt) {
System.out.println("Found " + searchfor +
" at " + i + ", " + j);
} else {
System.out.println(searchfor
+ " not in the array");
}
}
}

The continue Statement
The continue statement skips the current iteration of a for, while , or do-while loop. The unlabeled
form skips to the end of the innermost loop's body and evaluates the boolean expression that
controls the loop.
class ContinueDemo {
String searchMe = "peter piper picked a peck of pickled peppers";
int max = searchMe.length();
int numPs = 0;
for (int i = 0; i < max; i++) {
//interested only in p's
if (searchMe.charAt(i) != 'p')
continue;
numPs++;
}
System.out.println("Found " + numPs + " p's in the string.");
}
}
Found 9 p's in the string.

LAB - ContinueWithLabelDemo
class ContinueWithLabelDemo {
String searchMe = "Look for a substring in me";
String substring = "sub";
int max = searchMe.length() - substring.length();
test:
for (int i = 0; i <= max; i++) {
int n = substring.length();
int j = i;
int k = 0;
while (n-- != 0) {
if (searchMe.charAt(j++)
!= substring.charAt(k++)) {
continue test;
}
}
foundIt = true;
break test;
}
System.out.println(foundIt ? "Found it" :
"Didn't find it");
}
}
A labeled continue statement skips the current iteration of an outer loop marked with the given label. The following example
program, ContinueWithLabelDemo, uses nested loops to search for a substring within another string. Two nested loops are
required: one to iterate over the substring and one to iterate over the string being searched. The following program,
ContinueWithLabelDemo, uses the labeled form of continue to skip an iteration in the outer loop.
Found it

The return Statement
The return statement has two forms: one that returns a value, and one that
doesn't. To return a value, simply put the value (or an expression that calculates
the value) after the return keyword.
return countResult;
The data type of the returned value must match the type of the method's declared
return value. When a method is declared void, use the form of return that doesn't
return a value.
return;
The Classes and Objects lesson will cover everything you need to know about
writing methods.

Java Exceptions Handling
When an error occurs within a method, the method creates an object and
hands it off to the runtime system. The object, called an exception object,
contains information about the error, including its type and the state of the
program when the error occurred. Creating an exception object and
handing it to the runtime system is called throwing an exception.
Method Call Exception Call

LAB - DivideException1
public class DivideException1 {
static int quotient = -1;
int result = division(100, 0); // Line 2
System.out.println("result : " + result);
}
public static int division(int totalSum, int totalNumber) {
System.out.println("Computing Division.");
try {
quotient = totalSum / totalNumber;
} catch (Exception e) {
System.out.println("Exception : " + e.getMessage());
} finally {
if (quotient != -1) {
System.out.println("Finally Block Executes");
System.out.println("Result : " + quotient);
} else {
System.out.println("Finally Block Executes. Exception Occurred");
}
}
return quotient;
}
}
Computing Division.
Exception : / by zero
Finally Block Executes. Exception Occurred
result : -1

LAB – DivideException2
public class DivideException2 {
static int quotient = -1;
try {
int result = division(100, 0); // Line 2
System.out.println("result : " + result);
} catch (Exception e) {
System.out.println("Exception : " + e.getMessage());
} finally {
if (quotient != -1) {
System.out.println("Finally Block Executes");
System.out.println("Result : " + quotient);
} else {
System.out.println("Finally Block Executes. Exception
Occurred");
}
}
}
public static int division(int totalSum,
int totalNumber) throws Exception {
System.out.println("Computing Division.");
quotient = totalSum / totalNumber;
return quotient;
}
}
Computing Division.
Exception : / by zero
Finally Block Executes.
Exception Occurred

Danairat T.
Line ID: Danairat
FB: Danairat Thanabodithammachari
+668-1559-1446
Thank you

Java Programming - 03 java control flow

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