Doubly Linked List In java || Implement DLL Data Structure

[ravipankaj]

package com.ds.algorithms.linkedlist.DLLImplementation;

import java.util.NoSuchElementException;

/**
* @Author pankaj
* @create 4/12/21 7:05 PM
*/
public class DoublyLinkedList {
private Node head;// first node of DLL
private Node tail;//Last Node of DLL
private int length;// length of DLL

private class Node{
private int data;
private Node next;
private Node previous;
Node(int data) {
this.data=data;
}
}
// constructor
DoublyLinkedList()
{
this.head=null;
this.tail=null;
this.length=0;
}
// isEmpty()
// two ways to check , DLL is Empty 1. By checking head ref 2. By checking DLL length is zero(0)
public boolean isEmpty()
{
if(head==null)
return true;
else return false;
// return length==0;// DLL is empty-> true
}
//length() of DLL
public int length()
{
return length;
}

//------------------- print DLL in Forward Direction -----------------------
public void printDLLForward()
{
if (head==null) {
return;
}
Node traverse=head;
while (traverse !=null)
{
System.out.print(traverse.data+" --> ");
traverse=traverse.next;
}
System.out.println("null");
}
// ------------------------ print DLL in Backward Direction ----------------------
public void printDLLBackward()
{
if (tail==null) {
return;
}
Node traverse=tail;
while (traverse !=null)
{
System.out.print(traverse.data+" --> ");
traverse=traverse.previous;
}
System.out.println("null");
}
//------------------- insertFirst ---------------------
public void insertFirst(int data){
Node newNode=new Node(data);
if (isEmpty())
{
tail=newNode;
}else {
head.previous=newNode; //========
}
newNode.next=head;
head=newNode;
length++;
}

// -----------------insertLast ------------------------------------------
public void insertLast(int data)
{
Node newNode=new Node(data);
if (isEmpty())
{
head=newNode;// head is constant
} else {
tail.next=newNode;//--------
newNode.previous=tail;
}
tail=newNode;
length++;
}
// -------------------------------delete First ------------------------------
public Node deleteFirst()
{
if (isEmpty())
{
throw new NoSuchElementException("DLL is Already Empty !!!!");
}
Node newNode= head;
if (head == tail)
{
tail=null;
} else {
head.next.previous=null;
}
head=head.next;
newNode.next=null;
length--;
return newNode;
}
// ------------------ delete Last -------------------------
public Node deleteLast()
{
if(isEmpty()) {
throw new NoSuchElementException();
}
Node newNode=tail;
if (head==tail)
{
head=null;
} else {
tail.previous.next=null;
}
tail= tail.previous;
newNode.previous=null;
length--;
return newNode;
}
public static void main(String[] args) {
DoublyLinkedList dll=new DoublyLinkedList();
/*dll.insertFirst(0);
dll.insertFirst(1);
dll.insertFirst(5);
dll.insertFirst(7);
dll.insertFirst(9);
dll.insertFirst(12);
dll.printDLLForward();*/
// dll.printDLLBackward();

dll.insertLast(1);
dll.insertLast(2);
dll.insertLast(3);
dll.insertLast(4);
dll.insertLast(5);

dll.printDLLForward();
dll.printDLLBackward();
System.out.println("----------------------------------------");
// dll.deleteFirst();
//dll.printDLLForward();
// dll.deleteFirst();
// dll.deleteFirst();
dll.deleteLast();
dll.printDLLForward();
}
}