Collection framework

Collection framework

 It is introduced in java 2 before to that there are five legacy classes and one legacy interface

               Vector

               HashTable

               Properties             legacy classes                 Eenumeration                 legacy interface

               Dictionary

               Stack

 There are some problem in above listed legacy classes to avoid these problem Sun has introduced collection framework in Java 2.

In the collection frame work there are the three different category:--------

List :----- collection of object with duplicate.

Set :----- collection of object without duplicate.

Map :--- collection of key value pairs

List interface three concrete subclasses :-----------

Array list

Vector

Linked list

Array list :---------

Array list is subclass of list. Array list elements will be stored internally with indexing notation.

Because of implementing random access marker interface you can access the array list element randomly.

Because of implementing cloneable,  serializable marker interfaces ,array list object is eligible for cloning and serialization.

Array list objects are not synchronized by defaults.

Synchronization means  we can  enforce locking mechanism.

Let us try to understand with a example:

import java.util.*;

class altest

{

public static void main(String as[])

{

ArrayList al=new ArrayList();

al.add(new Integer(99));

al.add("JAVA");

al.add(new String("java@yahoo.com"));

System.out.println(al);

}

}

Output:

99, JAVA, java@yahoo.com

import java.util.*;

class al1

{

public static void main(String as[])

{

ArrayList al=new ArrayList();

al.add(new Integer(99));

al.add("JAVA");

al.add(new String("java@yahoo.com"));

System.out.println(al);

Iterator i=al.iterator();

while(i.hasNext())

{

String str=i.next().toString();

System.out.println(str);

}          }           }

/*

Output:

99, JAVA, java@yahoo.com

99

java

java@yahoo.com

Difference between array list and vector

Array list   Array list is collection class. Which is implementing marker interface like cloneable, serializable and random access    Objects of array list are not synchronized by default, i.e. multiple threads can access array list objects concurrently    You can access array list elements using Iterator.

Vector Vector is a legacy class which is also implementing same three interface.    Vector class object are synchronized by default i.e. only one thread can access vector class object at a time .Remaining threads as to wait until thread usage is completed.   You can access vector elements using Iterator or Enumeration.

Difference between iterator and list iterator

Iterator Using iterator you can visit the elements of collection in the forward direction only   Using iterator you cannot add elements to collection    Using iterator you can not replace existing object with new object.    Using iterator you can not get index of elements

List Iterator In list iterator you can visit the elements of collection in the forward and backward direction.    Using list Iterator you can add elements to collection.    Using iterator you can  replace existing object with new object.    Using list Iterator you get index of  elements  list

Note: ---using both we can remove the elements from the collection.

Difference between iterator and enumeration: --------------

Iterator Iterator is a collection framework.    Using iterator you can read elements of collection and also you can add elements, update element, read elements and remove elements. You can use iterator to access the elements of Array list, Vector, Linked list, HashSet ,TreeSet, LinkedHashSet.

Enumeration  Enumeration is a legacy interface    Using enumeration only you can read the elements.    You can use enumeration to access the elements of vector only