Doubly

DoublyLinkedList.java

package LinkedList;

class node
{
    int data;
    node next;
    node prev;
    public node(int data)
    {
        this.data = data;
        next = prev=null;
    }
}
public class DoublyLinkedList {

    node head;
    node tail;
    int length=0;
    public DoublyLinkedList()
    {
        head = tail = null;
    }

     public boolean isEmpty()
     {
         if (head == null)         //return length =0;
             return true;
         else
             return false;
     }


     //insert
    public void insert(int data)
    {
        node newnode = new node(data);
        if (isEmpty())
        {
            newnode.next = head;
            newnode.prev = null;
            head = newnode;
            tail = newnode;
        }
        else {

//            tail.next = newnode;
//            newnode.prev = tail;
//            tail = newnode;

            node temp = head;
            while (temp.next!=null)
            {
                temp  = temp.next;

            }
            temp.next= newnode;
            newnode.prev = temp;
        }
    }
    public void  insertafternode(node prevnode,int data)
    {
        node newnode = new node(data);

        newnode.next = prevnode.next;
        prevnode.next = newnode;
        newnode.prev = prevnode;


    }


    public void pint()
    {
        node temp =head;
        node tail = null;
        System.out.println("forward");
        while(temp!=null)
        {
            System.out.print(temp.data + " ");
            tail = temp;
            temp=temp.next;
        }
        System.out.println();
        System.out.println("backward");

        while (tail!=null)
        {
            System.out.print(tail.data + " ");
            tail=tail.prev;
        }
    }
}

class test12
{
    public static void main(String[] args) {

        DoublyLinkedList obj = new DoublyLinkedList();
        obj.insert(10);
        obj.insert(20);
        obj.insert(30);
        obj.insert(40);

        obj.insertafternode(obj.head.next,25);
        obj.pint();

    }
}