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

 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 is this list changes after the operation otherwise returns 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 the 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 codesjava
 */
public class ArrayListTest {
	public static void main(String args[]){
		//Create ArrayList object.
		List arrayList = new ArrayList();
 
		//Add objects to the HashSet.
		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 the specific position.
		arrayList.add(2,"Jagdeep");
 
		//Remove a 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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