LinkedList

Basic Structure of a Linked List :

Like arrays, Linked List is a linear data structure. Unlike arrays, linked list elements are not stored at the contiguous location, the elements are linked using pointers.

class LinkedList
{
    Node head;  //Head of list
    class Node   //Node class
    {
        int data;
        Node next;
        Node(int d)
        {
            data=d;
            next=null;
        }
    }
}

Initializing a List in Java

List is an interface, and the instances of List can be created in the following ways:

• List a = new ArrayList();
• List b = new LinkedList();
• List c = new Vector();
• List d = new Stack();

Below are the following ways to initialize a list:

1. Using List.add() method

public static void main(String[] args){
    // For ArrayList
    List<Integer> list = new ArrayList<Integer>();
    list.add(1);
    list.add(3);
    System.out.println("ArrayList : " + list.toString());

    // For LinkedList
    List<Integer> llist = new LinkedList<Integer>();
    llist.add(2);
    llist.add(4);
    System.out.println("LinkedList : " + llist.toString());

    // For Stack
    List<Integer> stack = new Stack<Integer>();
    stack.add(3);
    stack.add(1);
    System.out.println("Stack : " + stack.toString());

    }

    /*
    Output :
    ArrayList : [1, 3]
    LinkedList : [2, 4]
    Stack : [3, 1]

    */

• Double Brace Initialization can also be used to do the above work.

public static void main(String args[])
{

    // For ArrayList
    List<Integer> list = new ArrayList<Integer>() {{
        add(1);
        add(3);
        } };
    System.out.println("ArrayList : " + list.toString());

    // For LinkedList
    List<Integer> llist = new LinkedList<Integer>() {{
        add(2);
        add(4);
        } };
    System.out.println("LinkedList : " + llist.toString());

    // For Stack
    List<Integer> stack = new Stack<Integer>() {{
        add(3);
        add(1);
        } };
    System.out.println("Stack : " + stack.toString());
}

/*

Output:
ArrayList : [1, 3]
LinkedList : [2, 4]
Stack : [3, 1]

*/

2. Using Arrays.asList()

Creating Immutable List

• Arrays.asList() creates an immutable list from an array. Hence it can be used to instantiate a list with an array.

List<Integer> list=Arrays.asList(1, 2, 3);

• Example :

public static void main(String args[])
{

    // Instantiating List using Arrays.asList()
    List<Integer> list = Arrays.asList(1, 2, 3);

    // Print the list
    System.out.println("List : " + list.toString());
}

/*
Output:
List : [1, 2, 3]
*/

Creating Mutable List

List<Integer> list=new ArrayList<>(Arrays.asList(1, 2, 3));

• Example :

public static void main(String args[])
{

    // Creating a mutable list using Arrays.asList()
    List<Integer> list = new ArrayList<>(
        Arrays.asList(1, 2, 3));

    // Print the list
    System.out.println("List : " + list.toString());

    list.add(5);

    // Print the list
    System.out.println("Modified list : " + list.toString());
}

/*

Output :
List : [1, 2, 3]
Modified list : [1, 2, 3, 5]

*/

3. Using Collections.addAll()

public static void main(String args[])
{

    // Create an empty list
    List<Integer> list = new ArrayList<Integer>();

    // Instantiating list using Collections.addAll()
    Collections.addAll(list, 1, 2, 3, 4);

    // Print the list
    System.out.println("List : " + list.toString());
}

/*

Output:
List : [1, 2, 3, 4]

*/