DoublyLL.java

public class DoublyLL {
    public class Node{
        int data;
        Node next;
        Node prev;
        public Node(int data){
            this.data = data;
            this.next=null;
            this.prev=null;
        }
    }
    public static Node head;
    public static Node tail;
    public static int size;

    //add
    public void addFirst(int data){
        Node newNode = new Node(data);
        if(head==null){
            head=tail=newNode;
            return;
        }
        newNode.next = head;
        head.prev = newNode;
        head = newNode;
    }
    //remove
    public int removeFirst(){
        if(head==null){
            System.out.println("Empty list");
            return Integer.MIN_VALUE;
        }
        if(size==1){
            int val = head.data;
            head = null;
            tail = null;
            size-- ;
            return val;

        }
        int val = head.data;
        head = head.next;
        head.prev = null;
        return val;
    }
    public void reverse(){
        Node curr = head;
        Node prev = null;
        Node next;
        while(curr!=null){
            next = curr.next;
            curr.next = prev;
            curr.prev = next;

            prev = curr;
            curr = next;
        }
        head = prev;

    }
    public void print(){
        Node temp = head;
        while(temp !=null){
            System.out.print(temp.data + "<->");
            temp = temp.next;
        }
        System.out.println("null");
    }

    public static void main(String[] args) {
        DoublyLL dll =  new DoublyLL();
        dll.addFirst(3);
        dll.addFirst(2);
        dll.addFirst(1);
        dll.print();
        dll.removeFirst();
        dll.print();
        dll.reverse();
        dll.print();

    }
    
}