LinkedList in Java:  Methods

• The LinkedList class in Java provides us with the doubly linked list data structure.
• Each element of the linked list is known as a node.
• Each node points to the address of the next node & its previous node.

• Linked lists are preferred over the Array list because the insertion & deletion in the linked lists can be done in a constant time. But, in arrays, if we want to add or delete an element in between then, we need to shift all the other elements.
• In a linked list, it is impossible to directly access an element because we need to traverse the whole linked list to get the desired element.

ArrayList Vs. LinkedList :

Although ArrayList & LinkedList both implement the List interface and have the same methods, it is important to understand when to use which one.

• The insertion & deletion can be done in constant time in Linked List, so it is best to use the linked list when you need to add or remove elements frequently.
• Use ArrayList when you want to access the random elements frequently, as it can’t be done in a linked list in constant time.

Performing various operations on LinkedList :

1. Adding Element in LinkedList:

   • Similar to ArrayList, add() method is used to add elements in a linked list.
   • add(Object): Inserts an element at the end of the ArrayList.
   • add(Index,Object) : Inserts an element at the given index.
     Example :
     

     import java.util.*;
     public class CWH extends Thread{
         public static void main(String[] args) {
     
             LinkedList<Integer> l1 = new LinkedList<>();
     
             l1.add(11);
             l1.add(22);
             l1.add(33);
             l1.add(44);
             l1.add(55);
             l1.add(77);
             l1.add(5,77); // Inserts 77 at index 5
             System.out.println("L1 Linked list : "+ l1);
     
         }
     }

Output :

L1 Linked list : [11, 22, 33, 44, 55, 77, 77]

Removing an element from the LinkedList:

• remove() method is used to remove an element from the linked list.
  

  Example :

  import java.util.*;
  public class CWH extends Thread{
      public static void main(String[] args) {
  
          LinkedList<Integer> l1 = new LinkedList<>();
  
          l1.add(11);
          l1.add(22);
          l1.add(33);
          l1.add(44);
          l1.add(55);
          l1.add(77);
          l1.add(5,77); 
          System.out.println("L1 Linked list before: "+ l1);
  
          l1.remove(2); //removes element present at 2nd index
          System.out.println("L1 Linked list after: "  + l1);
  
      }
  }
  

Output :

L1 Linked list before: [11, 22, 33, 44, 55, 77, 77]
L1 Linked list after: [11, 22, 44, 55, 77, 77]

Changing An Element Of Linked List :

• set() method is used to change an already existing element of a linked list.

  Example :

  import java.util.*;
  public class CWH extends Thread{
      public static void main(String[] args) {
  
          LinkedList<Integer> l1 = new LinkedList<>();
  
          l1.add(11);
          l1.add(22);
          l1.add(33);
          l1.add(44);
          l1.add(55);
          l1.add(66);
          System.out.println("L1 Linked list before: "+ l1);
  
          l1.set(2,10); //changes element present at 2nd index (33 changed to 10)
          System.out.println("L1 Linked list after: "  + l1);
  
      }
  }
  

Output :

L1 Linked list before: [11, 22, 33, 44, 55, 66]
L1 Linked list after: [11, 22, 10, 44, 55, 66]

Inserting an element at the last of the linked list:

• addlast() method is used to insert an element at the start of the linked list.

  Example :

  F.	import java.util.*;
  public class CWH extends Thread{
      public static void main(String[] args) {
  
          LinkedList<Integer> l1 = new LinkedList<>();
  
          l1.add(11);
          l1.add(22);
          l1.add(33);
          l1.add(44);
          l1.add(55);
          l1.add(66);
          System.out.println("L1 Linked list before: "+ l1);
  
          l1.addLast(100); //Inserting 100 at the end of L1
          System.out.println("L1 Linked list after inserting element at last index: "  + l1);
  
      }
  }
  

Output :

L1 Linked list before: [11, 22, 33, 44, 55, 66]
L1 Linked list after inserting element at last index: [11, 22, 33, 44, 55, 66, 100]

Inserting an element at the start of the linked list:

• addFirst() method is used to insert an element at the start of the linked list.

  Example :

  import java.util.*;
  public class CWH extends Thread{
      public static void main(String[] args) {
  
          LinkedList<Integer> l1 = new LinkedList<>();
  
          l1.add(11);
          l1.add(22);
          l1.add(33);
          l1.add(44);
          l1.add(55);
          l1.add(66);
          System.out.println("L1 Linked list before: "+ l1);
  
          l1.addFirst(0); //Inserting 0 at the starting of L1
          System.out.println("L1 Linked list after: "  + l1);
  
      }
  }
  

Output :

L1 Linked list before: [11, 22, 33, 44, 55, 66]
L1 Linked list after: [0, 11, 22, 33, 44, 55, 66]

Code as described/written in the video :

package com.company;

import java.util.*;

public class cwh_92_linkedlist {
    public static void main(String[] args) {
        LinkedList<Integer> l1 = new LinkedList<>();
        LinkedList<Integer> l2 = new LinkedList<>();
        l2.add(15);
        l2.add(18);
        l2.add(19);

        l1.add(6);
        l1.add(7);
        l1.add(4);
        l1.add(6);
        l1.add(0, 5);
        l1.add(0, 1);
        l1.addAll(0, l2);
        l1.addLast(676);
        l1.addFirst(788);
        System.out.println(l1.contains(27));
        System.out.println(l1.indexOf(6));
        System.out.println(l1.lastIndexOf(6));
        //l1.clear();
        l1.set(1, 566);
        for(int i=0; i<l1.size(); i++){
            System.out.print(l1.get(i));
            System.out.print(", ");
        }
    }
}