DoublyLinkedList.java

import java.util.Scanner;
public class DoublyLinkedList {
    class Node {
        int data;
        Node prev, next;
        Node(int d) {
            data=d;
            prev=null;
            next=null;
        }}
    Node head = null;
    void insertFront(int data) {
        Node newNode = new Node(data);
        if (head==null) {
            head=newNode;
        } else {
            newNode.next = head;
            head.prev = newNode;
            head = newNode;
        }}
    void insertBack(int data) {
        Node newNode = new Node(data);
        if (head == null) {
            head = newNode;
        } else {
            Node temp = head;
            while (temp.next != null) {
                temp = temp.next;
            }
            temp.next = newNode;
            newNode.prev = temp;
        }}
    void deleteFront() {
        if (head == null) {
            System.out.println("List is empty");
            return;
        } else {
            System.out.println(head.data + " deleted");
            head = head.next;
            if (head != null) {
                head.prev = null;
            }}}
    void deleteBack() {
        if (head == null) {
            System.out.println("List is empty!");
        } else if (head.next == null) {
            System.out.println(head.data + " deleted");
            head = null;
        } else {
            Node temp = head;
            while (temp.next != null) {
                temp = temp.next;
            }
            System.out.println(temp.data + " deleted");
            temp.prev.next = null;
        }}
    void display() {
        Node temp=head;
        Node last=null;
        if (temp == null) {
            System.out.println("List is empty");
        } else {
            System.out.println("Double Linked List: ");
            while (temp != null) {
                System.out.print(temp.data + "->");
                last = temp;
                temp = temp.next;
            }
            System.out.println("NULL");
            System.out.println("\nPrint in reverse: ");
            while (last != null) {
                System.out.print(last.data + "->");
                last = last.prev;
            }
            System.out.println("START");
        }}
        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            DoublyLinkedList dll = new DoublyLinkedList();
            int choice, value;
            while (true) {
                System.out.println("\n1. Insert at Beginning");
                System.out.println("2. Insert at End");
                System.out.println("3. Delete from Beginning");
                System.out.println("4. Delete from End");
                System.out.println("5. Display");
                System.out.println("6. Exit");
                System.out.print("Enter your choice: ");
                choice = sc.nextInt();
                switch (choice) {
                    case 1:
                        System.out.print("Enter value: ");
                        value = sc.nextInt();
                        dll.insertFront(value);
                        break;
                    case 2:
                        System.out.print("Enter value: ");
                        value = sc.nextInt();
                        dll.insertBack(value);
                        break;
                    case 3:
                        dll.deleteFront();
                        break;
                    case 4:
                        dll.deleteBack();
                        break;
                    case 5:
                        dll.display();
                        break;
                    case 6:
                        System.out.println("Exiting...");
                        return;
                    default:
                        System.out.println("Invalid choice!");
                }}}}