DLL.java

public class DLL {
    Node head; // head of list
    class Node {
        int data;
        Node prev;
        Node next;
        Node(int d) { data = d; }
    }
    public void push(int new_data)
    {
        Node new_Node = new Node(new_data);
        new_Node.next = head;
        new_Node.prev = null;
        if (head != null)
            head.prev = new_Node;
        head = new_Node;
    }
   
    public void InsertBefore(Node next_node, int new_data)
    {
        if(next_node == null)
        {
            System.out.println("The given next node can not be NULL");
            return;
        }
         
        Node new_node = new Node(new_data);
        new_node.prev = next_node.prev;
         
        next_node.prev = new_node;
        new_node.next = next_node;
         
        if(new_node.prev != null)
            new_node.prev.next = new_node;
        else
            head = new_node;
    }
 
    public void InsertAfter(Node prev_Node, int new_data)
    {
 
        if (prev_Node == null) {
            System.out.println("The given previous node cannot be NULL ");
            return;
        }
 
        Node new_node = new Node(new_data);
 
        new_node.next = prev_Node.next;
        prev_Node.next = new_node;
        new_node.prev = prev_Node;
 
        if (new_node.next != null)
            new_node.next.prev = new_node;
    }
 
    void append(int new_data)
    {
        Node new_node = new Node(new_data);
 
        Node last = head;
        new_node.next = null;

        if (head == null) {
            new_node.prev = null;
            head = new_node;
            return;
        }
        while (last.next != null)
            last = last.next;
 
        last.next = new_node;
 
        new_node.prev = last;
    }
 
    public void printlist(Node node)
    {
        Node last = null;
        System.out.println("Traversal in forward Direction");
        while (node != null) {
            System.out.print(node.data + " ");
            last = node;
            node = node.next;
        }
        System.out.println();
        System.out.println("Traversal in reverse direction");
        while (last != null) {
            System.out.print(last.data + " ");
            last = last.prev;
        }
    }

    void deleteNode(Node del)
    {
 
        // Base case
        if (head == null || del == null) {
            return;
        }
        if (head == del) {
            head = del.next;
        }
 
        if (del.next != null) {
            del.next.prev = del.prev;
        }
 
        if (del.prev != null) {
            del.prev.next = del.next;
        }
 
        return;
    }
 
    public static void main(String[] args)
    {
        DLL dll = new DLL();
 
        dll.append(6);

        // Insert at the beginning. So
        dll.push(7);
        dll.push(1);

        //inert at end
        dll.append(4);

        
        dll.InsertAfter(dll.head.next, 8);
       
        dll.InsertBefore(dll.head.next.next, 5);
 
        System.out.println("Created DLL is: ");
        dll.printlist(dll.head);


        dll.deleteNode(dll.head);
 
        System.out.print("\nList after deleting first node: ");
        dll.printlist(dll.head);
 
        dll.deleteNode(dll.head.next);
 
        System.out.print("\nList after Deleting middle node: ");
        dll.printlist(dll.head);
    }
}