Difference between Singly linked list and Doubly linked list in Java

Java 8 Object Oriented Programming Programming

Both Singly linked list and Doubly linked list are the implementation of Linked list in which every element of singly-linked list contains some data and a link to the next element, which allows to keep the structure. On the other hand, every node in a doubly-linked list also contains a link to the previous node.

The following are the important differences between a Singly linked list and Doubly linked list.

Sr. No.	Key	Singly linked list	Doubly linked list
1	Complexity	In singly linked list the complexity of insertion and deletion at a known position is O(n)	In case od doubly linked list the complexity of insertion and deletion at a known position is O(1)
2	Internal implementation	In singly linked list implementation is such as where the node contains some data and a pointer to the next node in the list	While doubly linked list has some more complex implementation where the node contains some data and a pointer to the next as well as the previous node in the list
3	Order of elements	Singly linked list allows traversal elements only in one way.	Doubly linked list allows element two way traversal.
4	Usage	Singly linked list are generally used for implementation of stacks	On other hand doubly linked list can be used to implement stacks as well as heaps and binary trees.
5	Index performance	Singly linked list is preferred when we need to save memory and searching is not required as pointer of single index is stored.	If we need better performance while searching and memory is not a limitation in this case doubly linked list is more preferred.
6	Memory consumption	As singly linked list store pointer of only one node so consumes lesser memory.	On other hand Doubly linked list uses more memory per node(two pointers).

Example of Singly linked list vs Doubly linked list

SinlgyLinkedList.java

class Node {
   //create class Node
   public int data;
   public Node next; //create node parameter for pointer of next element
   public void displayNodeData() {
      System.out.println("{ " + data + " } ");
   }
}
public class SinglyLinkedList {
   private Node head;
   public boolean isEmpty() {
      return (head == null);
   }
   // used to insert a node at the start of linked list
   public void insertFirst(int data) {
      Node newNode = new Node();
      newNode.data = data;
      newNode.next = head;
      head = newNode;
   }
   // used to delete node from start of linked list
   public Node deleteFirst() {
      Node temp = head;
      head = head.next;
      return temp;
   }
   // Use to delete node after particular node
   public void deleteAfter(Node after) {
      Node temp = head;
      while (temp.next != null && temp.data != after.data) {
         temp = temp.next;
      }
      if (temp.next != null)
      temp.next = temp.next.next;
   }
   // used to insert a node at the start of linked list
   public void insertLast(int data) {
      Node current = head;
      while (current.next != null) {
         current = current.next; // we'll loop until current.next is null
      }
      Node newNode = new Node();
      newNode.data = data;
      current.next = newNode;
   }
   // For printing Linked List
   public void printLinkedList() {
      System.out.println("Printing LinkedList (head --> last) ");
      Node current = head;
      while (current != null) {
         current.displayNodeData();
         current = current.next;
      }
      System.out.println();
   }
}

Example

LinkedListMain.java

public class LinkedListMain {
   public static void main(String args[]){
      SinglyLinkedList myLinkedlist = new SinglyLinkedList();
      myLinkedlist.insertFirst(5);
      myLinkedlist.insertFirst(6);
      myLinkedlist.insertFirst(7);
      myLinkedlist.insertFirst(1);
      myLinkedlist.insertLast(2);
      Node node=new Node();
      node.data=1;
      myLinkedlist.deleteAfter(node);
      myLinkedlist.printLinkedList();
   }
}

Output

Printing LinkedList (head --> last)
{ 1 }
{ 6 }
{ 5 }
{ 2 }

Example

DoublyLinkedListMain.java

Live Demo

public class DoublyLinkedList {
   class Node{
      int data;
      Node previous;
      Node next;
      public Node(int data) {
         this.data = data;
      }
   }
   Node head, tail = null;
   public void addNode(int data) {
      //Create a new node
      Node newNode = new Node(data);
      if(head == null) {
         head = tail = newNode;
         head.previous = null;
         tail.next = null;
      } else {
         tail.next = newNode;
         newNode.previous = tail;
         tail = newNode;
         tail.next = null;
      }
   }
   public void display() {
      Node current = head;
      if(head == null) {
         System.out.println("List is empty");
         return;
      }
      System.out.println("Nodes of doubly linked list: ");
      while(current != null) {
         System.out.print(current.data + " ");
         current = current.next;
      }
   }
   public static void main(String[] args) {
      DoublyLinkedList dList = new DoublyLinkedList();
      dList.addNode(1);
      dList.addNode(2);
      dList.addNode(3);
      dList.addNode(4);
      dList.addNode(5);
      dList.display();
   }
}