• • Like ArrayList, LinkedList is another implementation class of List interface.
• • Underlying data structure is the double linked list.
• • >Duplicates are allowed.
• • Insertion order is preserved.
• • Null insertion is possible.
• • LinkedList implements Serializable and Clonable interface, but not RandomAccess interface.
• • If our frequent operation is the insertion and deletion in the middle, then LinkedListis the best choice.
• • If our frequent operation is the retrieval operation then LinkedList is the worst choice. Because here retrieval of data items is a time consuming process.
• • Usually we can use LinkedList to implement Stacks and Queues to provide support for this requirement. LinkedList class defines following specific methods:

voidaddFirst();
voidaddLast();
Object getFirst();
Object getLast();
Object removeFirst();
Object removeLast();

Constructors:

• • Creates an empty LinkedList Object.

  LinkedList l=new LinkedList();

• • Creates an equivalent LinkedList Object for the given Collection.

  LinkedList l=new LinkedList(Collection c);

Example:
LinkedListDemo.java:

import java.util.*;
class LinkedListDemo
{
	public static void main(String[] args)
	{
		LinkedList l=new LinkedList();
		l.add("Tapuuu");
		l.add("Mona");
		l.add("Divya");
		l.add(25);
		l.add(null);
		System.out.println(l);
		Iterator it=l.iterator();
		while(it.hasNext())
		{
			Object o1=it.next();
			System.out.println(o1);
		}
		l.addFirst("Tilan");
		l.addLast("Kandhei");
		System.out.println(l);
		l.remove(5);
		l.removeFirst();
		l.removeLast();
		System.out.println(l);
	}
}

Output

[Tapuuu,Mona,Divya,25,null]
Tapuuu
Mona
Divya
25
Null
[Tilan,Tapuuu,Mona,Divya,25,null,Kandhei]
[Tapuuu,Mona,Divya,25]

ArrayList vs. LinkedList:

ArrayList:

• • It is the best choice if our frequent operation is retrieval.
• • It is the worst choice if our frequent operation is insertion and deletion.
• • Underlying data structure for ArrayList is resizable or growable array.
• • It implements RandomAccess interface.

LinkedList:

• • It is the best choice if our frequent operation is insertion and deletion.
• • It is the worst choice if our frequent operation is retrieval operation.
• • Underlying data structure is double linked list.
• • It does not implement RandomAccess interface.