List interface in java

List interface:

A List represents an ordered or sequenced group of elements. It may contain duplicate elements. It extends the collection interface.  Note:

• Elements can be inserted or retrieved by their position in the list. Position or index value starts from 0.
• List interface defines its own methods in addition to the methods of collection interface.

List Interface declaration:

public interface List extends Collection

 Commonly used methods of List interface:

1. add(int index, Object obj): Insert obj at the specified index position into this list. All pre-existing elements at or beyond the specified index are shifted up.

Syntax:

public void add(int index, Object obj)

2. addAll(int index, Collection c): Insert all elements of the specified collection at the specified index position into this collection. All pre-existing elements at or beyond the specified index are shifted up. Returns true if this list changes after the operation otherwise return false.

Syntax:

public boolean addAll(int index, Collection c)

3. get(int index): Returns the object stored at specified index position into this list.

Syntax:

public Object get(int index)

4. indexOf(Object obj): Returns index of first occurrence of obj in this list. It returns -1 if obj is not exist in this list.

Syntax:

public int indexOf(Object obj)

5. lastIndexOf(Object obj): Returns index of last occurrence of obj in this list. It returns -1 if obj is not exist in this list.

Syntax:

public int lastIndexOf(Object obj)

6. listIterator( ): Returns an ListIterator object to the start of the this list.

Syntax:

public ListIterator listIterator( )

7. listIterator(int index): Returns an ListIterator object to this list that begins at the specified index.

Syntax:

public ListIterator listIterator(int index)

8. remove(int index): Removes the element at specified index position from this list and returns the deleted element. Indexes of all elements beyond index are decremented by one.

Syntax: public Object remove(int index)

9. set(int index, Object obj): Assigns obj to the specified index location within the this list.

Syntax:

public Object set(int index, Object obj)

10. subList(int start, int end): Returns a list that contains the elements from start to end-1 index position in this list.

Syntax:

public List subList(int start, int end)

 A simple example of ArrayList class to explain few methods of List interface.

 ArrayListTest.java

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
 
/**
 * This class is used to show the ArrayList functionality.
 * @author w3spoint
 */
public class ArrayListTest {
	public static void main(String args[]){
		//Create ArrayList object.
		List arrayList = new ArrayList();
 
		//Add objects to the List.
		arrayList.add("Amani");
		arrayList.add("Prabhjot");
		arrayList.add("Nidhi");
		arrayList.add("Vandana");
		arrayList.add("Poonam");
 
		//Size of the ArrayList object.
		System.out.println("Size: " 
				+ arrayList.size());
 
		//Print the ArrayList object.
		System.out.println("ArrayList elements:");
		System.out.println(arrayList);
 
		//Print the ArrayList elements using iterator.
		Iterator iterator1=arrayList.iterator();
		System.out.println("ArrayList elements " +
				"using iterator:");
		while(iterator1.hasNext()){  
		   System.out.println(iterator1.next());  
		} 
 
		//Add an object at a specific position.
		arrayList.add(2,"Jagdeep");
 
		//Remove an element from a specific position.
		arrayList.remove(3);
		arrayList.remove(4);
 
		//Size of the ArrayList object.
		System.out.println("Size after manipulation: "
				+ arrayList.size());
 
		//Print the ArrayList object.
		System.out.println("ArrayList elements" +
				" after manipulation:");
		System.out.println(arrayList);
 
		//Print the ArrayList elements using iterator.
		Iterator iterator2=arrayList.iterator();
		System.out.println("ArrayList elements after" +
				" manipulation using iterator:");
		while(iterator2.hasNext()){  
		   System.out.println(iterator2.next());  
		} 	
	}
}

Output:

Size: 5
ArrayList elements:
[Amani, Prabhjot, Nidhi, Vandana, Poonam]
ArrayList elements using iterator:
Amani
Prabhjot
Nidhi
Vandana
Poonam
Size after manipulation: 4
ArrayList elements after manipulation:
[Amani, Prabhjot, Jagdeep, Vandana]
ArrayList elements after manipulation using iterator:
Amani
Prabhjot
Jagdeep
Vandana

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