Java LinkedList class

The java.util.LinkedList class provides a doubly-linked list implementation of the interfaces named List and Deque.

It implements all optional list operations, and permits all elements (including null).

The operations that index into the list will traverse the list from the start or the end, whichever is closer to the specified index.

This class extends AbstractSequentialList and implements the List interface.

LinkedList Constructors

Following are the constructors supported by the LinkedList class.

LinkedList Methods

Apart from the methods inherited from its parent classes, LinkedList defines following methods −

Example

The following program illustrates different methods supported by the LinkedList class−

//LinkedListDemo.java

import java.util.Iterator;
import java.util.LinkedList;

public class LinkedListDemo {

    public static void main(String[] args) {
        //Create a LinkedList collection of Integers
        LinkedList<Integer> list = new LinkedList<Integer>();
        int size;
        Iterator<Integer> iterator;

        //Add data in the list
        list.add(11);
        list.add(22);
        list.add(33);
        list.add(44);
        size = list.size();
        System.out.print("Linked list data: ");

        //Create a iterator
        iterator = list.iterator();
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();

        //Check list empty or not
        if (list.isEmpty()) {
            System.out.println("Linked list is empty");
        } 
        else {
            System.out.println("Linked list size: " + size);
        }

        //Add at the first place
        list.addFirst(55);
        System.out.println("Adding data at first location: 55");
        System.out.print("Now the list contains: ");
        iterator = list.iterator();
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
        System.out.println("Now the size of list: " + list.size());

        //Adding last or append
        list.addLast(66);
        System.out.println("Adding data at last location: 66");
        System.out.print("Now the list contain: ");
        iterator = list.iterator();
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
        System.out.println("Now the size of list: " + list.size());

        //Adding data at 3rd position
        list.add(2, 99);
         System.out.println("Adding data at 3rd location: 99");
        System.out.print("Now the list contains: ");
        iterator = list.iterator();
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
        System.out.println("Now the size of list: " + list.size());

        //Retrieve first data
        System.out.println("First data: " + list.getFirst());

        //Retrieve last data
        System.out.println("Last data: " + list.getLast());

        //Retrieve specific data
        System.out.println("Data at position 3 is: " + list.get(3));

        //Remove first element
        int first = list.removeFirst();
        System.out.println("Data removed from 1st location: " + first);
        System.out.print("Now the list contains: ");
        iterator = list.iterator();

        //After removing data
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
        System.out.println("Now the size of list: " + list.size());

        //Remove last element
        int last = list.removeLast();
        System.out.println("Data removed from last location: " + last);
        System.out.print("Now the list contains: ");
        iterator = list.iterator();

        //After removing data
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
        System.out.println("Now the size of list: " + list.size());

        //Remove 2nd data
        int second = list.remove(1);
        System.out.println("Data removed from 2nd location: " + second);
        System.out.print("Now the list contains: ");
        iterator = list.iterator();

        //After removing data
        while (iterator.hasNext()) {
            System.out.print(iterator.next() + " ");
        }
        System.out.println();
        System.out.println("Now the size of list: " + list.size());

        //Remove all elements
        list.clear();
        if (list.isEmpty()) {
            System.out.println("Linked list is empty");
        } 
        else {
            System.out.println("Linked list size: " + size);
        }
    }
}

Output:

Linked list data: 11 22 33 44 
Linked list size: 4
Adding data at first location: 55
Now the list contains: 55 11 22 33 44 
Now the size of list: 5
Adding data at last location: 66
Now the list contain: 55 11 22 33 44 66 
Now the size of list: 6
Adding data at 3rd location: 99
Now the list contains: 55 11 99 22 33 44 66 
Now the size of list: 7
First data: 55
Last data: 66
Data at position 3 is: 22
Data removed from 1st location: 55
Now the list contains: 11 99 22 33 44 66 
Now the size of list: 6
Data removed from last location: 66
Now the list contains: 11 99 22 33 44 
Now the size of list: 5
Data removed from 2nd location: 99
Now the list contains: 11 22 33 44 
Now the size of list: 4
Linked list is empty