Collection Framework in Java | Generics | Input-Output in Java | Serialization | Inner Classes | Java class 4

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“Once a Programmer always a Programmer.”
•Collection Framework in Java
•Generics
•Input-Output in Java
•Serialization
•Inner Classes

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Collection Framework in Java

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Collections in Java
The Collection in Java is a framework that provides
an architecture to store and manipulate the group of
objects.
Java Collections can achieve all the operations that
you perform on a data such as searching, sorting,
insertion, manipulation, and deletion.
Java Collection means a single unit of objects. Java
Collection framework provides many interfaces (Set,
List, Queue, Deque) and classes (ArrayList,
Vector, LinkedList, PriorityQueue, HashSet,
LinkedHashSet, TreeSet).
Its come in java.util package.

Hierarchy of Collection Framework
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Methods of Collection interface
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And many more…

List Interface
List interface is the child interface of Collection
interface.
It inhibits a list type data structure in which we can
store the ordered collection of objects.
It can have duplicate values.
List interface is implemented by the classes
ArrayList, LinkedList, Vector, and Stack.
To instantiate the List interface
List <data-type> list1= new ArrayList();
List <data-type> list2 = new LinkedList();
List <data-type> list3 = new Vector();
List <data-type> list4 = new Stack();
Example: List <String> list = new ArrayList();
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ArrayList
The ArrayList class implements the List
interface.
It uses a dynamic array to store the duplicate
element of different data types.
The ArrayList class maintains the insertion
order and is non-synchronized.
The elements stored in the ArrayList class
can be randomly accessed.
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Array List Example
import java.util.*;
class TestJavaCollection1{
public static void main(String args[]){
ArrayList<String> list=new ArrayList<String>();//Creating arraylist
list.add("Ravi");//Adding object in arraylist
list.add("Vijay");
list.add("Ravi");
list.add("Ajay");
//Traversing list through Iterator
Iterator itr=list.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
}
}
}
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Output?

LinkedList
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•LinkedList implements the Collection interface.
•It uses a doubly linked list internally to store the
elements.
•It can store the duplicate elements.
•It maintains the insertion order and is not synchronized.
•In LinkedList, the manipulation is fast because no
shifting is required.

Example
import java.util.*;
public class TestJavaCollection2{
LinkedList<String> al=new LinkedList<String>();
al.add("Ravi");
al.add("Vijay");
al.add("Ravi");
al.add("Ajay");
Iterator<String> itr=al.iterator();
}
}
}
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Vector - Stack
Vector uses a dynamic array to store the data elements.
It is similar to ArrayList.
It’s a legacy class . Why it is legacy class?
However, It is synchronized and contains many methods that
are not the part of Collection framework.
The stack is the subclass of Vector.
It implements the last-in-first-out data structure, i.e., Stack.
The stack contains all of the methods of Vector class and also
provides its methods like boolean push(), boolean peek(),
boolean push(object o), which defines its properties.
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Example
import java.util.*;
public class TestJavaCollection4{
Stack<String> stack = new Stack<String>();
stack.push("Ayush");
stack.push("Garvit");
stack.push("Amit");
stack.push("Ashish");
stack.push("Garima");
stack.pop();
Iterator<String> itr=stack.iterator();
}
}
}
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Output??

Queue Interface
Queue interface maintains the first-in-first-out
order.
It can be defined as an ordered list that is used to
hold the elements which are about to be processed.
There are various classes like PriorityQueue,
Deque, and ArrayDeque which implements the
Queue interface.
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Priority Queue
The PriorityQueue class implements the Queue interface.
It holds the elements or objects which are to be processed
by their priorities.
PriorityQueue doesn't allow null values to be stored in the
queue.
Deque:
Deque interface extends the Queue interface.
 In Deque, we can remove and add the elements from both
the side.
Deque stands for a double-ended queue which enables us
to perform the operations at both the ends.

ArrayDeque
ArrayDeque class implements the Deque interface.
It facilitates us to use the Deque.
Unlike queue, we can add or delete the elements
from both the ends.
ArrayDeque is faster than ArrayList and Stack and
has no capacity restrictions.
Deque<String> deque = new ArrayDeque<String>();
deque.add("Gautam");
deque.add("Karan");
deque.add("Ajay");
for (String str : deque) { //Traversing elements
System.out.println(str);
}
}
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Output?

Set Interface
 Set Interface in Java is present in java.util package.
 It extends the Collection interface.
 It represents the unordered set of elements which
doesn't allow us to store the duplicate items.
 We can store at most one null value in Set.
 Set is implemented by HashSet, LinkedHashSet,
and TreeSet.
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HashSet class implements Set Interface.
It represents the collection that uses a hash table for storage.
Hashing is used to store the elements in the HashSet.
It contains unique items.
LinkedHashSet class represents the LinkedList implementation
of Set Interface.
It extends the HashSet class and implements Set interface.
Like HashSet, It also contains unique elements.
It maintains the insertion order and permits null elements.
SortedSet is the alternate of Set interface that provides a total
ordering on its elements.
The elements of the SortedSet are arranged in the increasing
(ascending) order.
The SortedSet provides the additional methods that inhibit the
natural ordering of the elements.
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Java TreeSet class implements the Set interface that uses a
tree for storage.
Like HashSet, TreeSet also contains unique elements.
However, the access and retrieval time of TreeSet is quite fast.
The elements in TreeSet stored in ascending order.
public void setexample(){
// same way we can used HashSet()<>, LinkedHashSet()<>
TreeSet<String> set=new TreeSet<String>();
set.add("Ravi");
set.add("Vijay");
set.add("Ravi");
set.add("Ajay");
//traversing elements
Iterator<String> itr=set.iterator();
}
}
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Java Map Interface
A map contains values on the basis of key, i.e. key-value pair.
Each key and value pair is known as an entry.
A Map contains unique keys.
A Map is useful if you have to search, update or delete
elements on the basis of a key.
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Class Description
HashMap HashMap is the implementation
of Map, but it doesn't maintain
any order.
LinkedHashMap LinkedHashMap is the
implementation of Map. It
inherits HashMap class. It
maintains insertion order.
TreeMap TreeMap is the implementation
of Map and SortedMap. It
maintains ascending order.
•A Map doesn't allow duplicate keys, but you can have duplicate
values.
•A Map can't be traversed, so you need to convert it into Set
using keySet() or entrySet() method.

Method Description
V put(Object key, Object value) It is used to insert an entry in the
map.
void putAll(Map map) It is used to insert the specified map
in the map.
V putIfAbsent(K key, V value) It inserts the specified value with the
specified key in the map only if it is
not already specified.
V remove(Object key) It is used to delete an entry for the
specified key.
boolean remove(Object key, Object
value)
It removes the specified values with
the associated specified keys from the
map.
Set keySet() It returns the Set view containing all
the keys.
Set<Map.Entry<K,V>> entrySet() It returns the Set view containing all
the keys and values.
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Example of Map
Public void MapExample(){
Map map=new HashMap();
//Adding elements to map
map.put(1,"Amit");
map.put(5,"Rahul");
map.put(2,"Jai");
map.put(6,"Amit");
//Traversing Map
Set set=map.entrySet();//Converting to Set so that we can traverse
Iterator itr=set.iterator();
//Converting to Map.Entry so that we can get key and value separately
Map.Entry entry=(Map.Entry)itr.next();
System.out.println(entry.getKey()+" "+entry.getValue());
} Java Values 22
Output?

Sorting collections using utility methods
Example :Collections.sort();
equals () and hash Code contract in Java collections
object value and there reference
Overriding equals and hash Code methods in Java.
To get the value which is save in hashmap or tree
map.
hashCode()
It returns the hashcode value as an Integer.
Hashcode value is mostly used in hashing based
collections like HashMap, HashSet,
HashTable….etc. This method must be overridden in
every class which overrides equals() method.
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Java Values.com
•The Java Generics programming is introduced in J2SE
5 to deal with type-safe objects.
•It makes the code stable by detecting the bugs at
compile time.
•Before generics, we can store any type of objects in the
collection, i.e., non-generic.
•Now generics force the java programmer to store a
specific type of objects.
•There are mainly 3 advantages of generics. They are as
follows:
1. Type-safety
2. Type casting is not required
3. Compile-Time Checking

Wildcard in Java Generics
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•The ? (question mark) symbol represents the wildcard
element. It means any type.
•If we write <? extends Number>, it means any child
class of Number, e.g., Integer, Float, and double.
•Now we can call the method of Number class through
any child class object.
•We can use a wildcard as a type of a parameter, field,
return type, or local variable.
•However, it is not allowed to use a wildcard as a
type argument for a generic method invocation, a
generic class instance creation, or a supertype.

import java.util.Arrays;
import java.util.List;
public class LowerBoundWildcard {
public static void addNumbers(List<? super Integer> list) {
for(Object n:list)
{
System.out.println(n);
}
}
public static void main(String[] args) {
List<Integer> l1=Arrays.asList(1,2,3);
System.out.println("displaying the Integer values");
addNumbers(l1);
List<Number> l2=Arrays.asList(1.0,2.0,3.0);
System.out.println("displaying the Number values");
addNumbers(l2);
}
}
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Output?

Serialization and Deserialization
Serialization in Java is a mechanism of writing the state of
an object into a byte-stream.
It is mainly used in Hibernate, RMI, JPA, EJB and JMS
technologies.
The reverse operation of serialization is
called deserialization where byte-stream is converted into
an object.
The serialization and deserialization process is platform-
independent, it means you can serialize an object in a
platform and deserialize in different platform.
For serializing the object, we call
the writeObject() method ObjectOutputStream, and for
deserialization we call the readObject() method
of ObjectInputStream class.
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import java.io.*;
class Persist{
try{
Student s1 =new Student(211,"ravi"); //Creating the object
FileOutputStream fout=new FileOutputStream("f.txt"); //Creating stream and writing the object
ObjectOutputStream out=new ObjectOutputStream(fout);
out.writeObject(s1);
out.flush(); //closing the stream
out.close();
System.out.println("success");
}catch(Exception e){System.out.println(e);}
}
}
import java.io.Serializable;
public class Student implements Serializable{
int id;
String name;
public Student(int id, String name) {
this.id = id;
this.name = name;
}
}
Output?

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import java.io.*;
class Depersist{
try{
//Creating stream to read the object
ObjectInputStream in=new ObjectInputStream(new FileInputStream("f.txt"));
Student s=(Student)in.readObject();
//printing the data of the serialized object
System.out.println(s.id+" "+s.name);
//closing the stream
in.close();
}catch(Exception e){System.out.println(e);}
}
}
import java.io.Serializable;
public class Student implements Serializable{
int id;
String name;
public Student(int id, String name) {
this.id = id;
this.name = name;
}
}
Output?

Inner Classes
Inner Classes
Local Classes
Anonymous Classes
Static Nested Classes
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Type Description
Member Inner Class A class created within class and
outside method.
Anonymous Inner Class A class created for implementing
interface or extending class. Its name
is decided by the java compiler.
Local Inner Class A class created within method.
Static Nested Class A static class created within class.
Nested Interface An interface created within class or
interface.
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Inner class is a part of nested class. Non-static nested
classes are known as inner classes.

Advantage of java inner classes
There are basically three advantages of inner
classes in java. They are as follows:
1) Nested classes represent a special type of
relationship that is it can access all the members
(data members and methods) of outer
class including private.
2) Nested classes are used to develop more
readable and maintainable code because it
logically group classes and interfaces in one place
only.
3) Code Optimization: It requires less code to
write.
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JAVA Input Output
The Stream is a sequence of Bytes.
Output Stream: Writing Data to a Stream.
Input Stream: Reading Data from a Stream.
If a stream has a buffer in memory then it is
Buffered Stream.
Character stream have character data and
are used for storing and retrieving the text.
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There are four types of abstract Streams
class
1. Reader: Read Character
2. Writer: Write Character
3. InputStream: A stream to read binary data.
4. OutputStream: A Stream to write binary data.
Generally we are using BufferedInputStream,
BufferedOutputStream, BufferedReader and
BufferedWriter for better performance of
Buffered I/O Classes.
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Byte Stream Classes
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Character Stream I/O Classes
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InputStream
Used to read binary data.
FileInputStream enables easy reading from a
file.
BufferInputStream provides data buffering .
InputStream class has three read method overloads.
1. public abstract int read(int b1)
2. public int read(byte[] data)
3. public int read(byte[] data, int offset, int length)
Where the offset stands for the first bytes should be
placed.
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The Predefined Streams
Java programs automatically import the java.lang package.
This package defines a class calledSystem, which
encapsulates several aspects of the run-time environment.
System also contains three predefined stream variables: in,
out, and err.
These fields are declared as public, static, and final within
System. This means that they can be used by any other part
of your program and without reference to a specific System
object.
System.in is an object of type InputStream;
System.out and System.err are objects of type
PrintStream. These are byte streams, even though they
typically are used to read and write characters from and to the
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File
File object is used to obtain or manipulate the information
associated with a disk file such as permission, time, date
and directory path.
File object can refer to either file or directory.
File f1 = new File(“mcaii.txt”);
File f1 = new File(“c:mcaii.txt”);
Files are stored in binary form.
The following constructors can be used to create
File objects:
File(String directoryPath)
File(String directoryPath, String filename)
File(File dirObj, String filename)
File(URI uriObj)
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FileInputStream
The FileInputStream class creates an InputStream that you can
use to read bytes from a file.
Its two most common constructors are shown here:
FileInputStream(String filepath)
FileInputStream(File fileObj)
FileOutputStream
FileOutputStream creates an OutputStream that you can use to
write bytes to a file.
Its most commonly used constructors are shown here:
FileOutputStream(String filePath)
FileOutputStream(File fileObj)
FileOutputStream(String filePath, boolean append)
FileOutputStream(File fileObj, boolean append)
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The PrintWriter Class
PrintWriter is one of the character-based classes.
Using a character-based class for console output makes it
easier to internationalize your program.
PrintWriter defines several constructors. The one we will
use is shown here:
PrintWriter(OutputStream outputStream, boolean
flushOnNewline)
Here, outputStream is an object of type OutputStream, and
flushOnNewline controls whether Java flushes the output
stream every time a println( ) method is called.
PrintWriter supports the print( ) and println( ) methods
for all types including Object.
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 The following application illustrates using a PrintWriter to
handle console output
// Demonstrate PrintWriter
import java.io.*;
public class PrintWriterDemo
{
public static void main(String args[])
{
PrintWriter pw = new PrintWriter(System.out, true);
pw.println("This is a string");
int i = -7;
pw.println(i);
double d = 4.5e-7;
pw.println(d);
}
}
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Reading and Writing Files
Two of the most often-used stream classes are
FileInputStream and FileOutputStream, which create byte
streams linked to files.
To open a file, you simply create an object of one of these
classes, specifying the name of the file as an argument to the
constructor.
The following are the forms that we will be using:
 FileInputStream(String fileName) throws FileNotFoundException
 FileOutputStream(String fileName) throws FileNotFoundException
DataOutputStream and DataInputStream
DataOutputStream and DataInputStream enable you to write
or read primitive data to or from a stream.
They implement the DataOutput and DataInput interfaces,
respectively.
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Summary
Collection Framework in Java
 The Collections Framework - Set Interface- List Interface - Map Interface -
Queue Interface -Sorting collections using utility methods
 equals () and hash Code contract in Java collections
 Overriding equals and hash Code methods in Java
Generics
 Generics for Collections, class and methods
Input-Output in Java
 What is a stream? ,Bytes vs. Characters, Java IO API ,Reading a file;
writing to a file using various APIs
 Reading User input from console , PrintWriter Class
Serialization
 Object Serialization , Serializable Interface , De-Serializable
Inner Classes
 Inner Classes ,Member Classes, Local Classes, Anonymous Classes,
Static Nested Classes
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Collection Framework in Java | Generics | Input-Output in Java | Serialization | Inner Classes | Java class 4

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