Who says java does not supports pointers part-4, implement QUEUE using linked list

Who says java does not supports pointers part-4, lets implement a Queue using linked list

This code of Queue is implemented by 

Vasu Gupta / IT / Maharaja Agrasen Institute of Technology

In this code the Queue is implemented using a linked list. 

# save this class inside Node.java file #

import java.util.Scanner;

//Create a node class for creating new nodes in linked list

class Node{

private int data ;  // data of that node

private Node next ; // node data of next linked node

public Node() { // initialize new node

data = 0 ;

next = null ;

}

// Input data in new node

public Node(int d , Node n) {

data = d ;

next = n ;

}

// set link to the next node

public void setLink(Node link) {

next = link ;

}

// Get link to the next node

public Node getLink() {

return next ;

}

// Get data of the current node

public int getData() {

return data ;

}

}

# save this class inside LinkList.java file #

//class for creating linked list

class LinkList {

private Node start ;

private Node end ;

public int front ;

public int rear ;

public int max ;

// Initialize all the variables

public LinkList() {

start = null ;

end = null ;

front = -1 ;

rear = -1 ;

max = 5 ;

}

// Adding nodes at last of the queue (Made up of linked list)

public void addAtEnd(int data) {

Node node = new Node(data , null); // Create object of Node class

// Check if queue is Full

if(rear == max -1) {

System.out.println("Queue is Full");

}else if(front == -1 && rear == -1){

front++ ; // Increment front by one

rear++ ; // Increment rear by one

start = node ; // make node the starting node

end = start ;  // make node the ending node

}else {

rear++ ;

end.setLink(node);  // Attach new node after end

end = node ; // make the new node as end 

}

}

// Deleting node in linked list

public void deleteNode() {

// Check if queue is empty

if(rear == -1) {

System.out.println("Empty Queue");

}else {

Node ptr = start ;

start = start.getLink();

ptr = null ;

front++ ;

}

}

// Function to show last element of the queue

public void showLastElement() {

// Check if queue is empty

if(rear == -1) {

System.out.println("Empty Queue");

}else {

System.out.println(end.getData());

}

}

// Function to show data of the queue

public void showData() {

if(start == null) {

System.out.println("No data");

}else { // Traverse through end of the queue and delete the last node of the queue      

Node ptr = start ;

while(ptr.getLink() != null) {

System.out.print(ptr.getData() + "--->");

ptr = ptr.getLink();

}

System.out.print(ptr.getData());

}

}

}

# save this class inside Queue.java file # 

public class Queue {

public static void main(String[] args) {

int data ;

LinkList ll = new LinkList();

// Create Scanner class object

Scanner sc = new Scanner(System.in);

// Get user input data again and again

do {

System.out.print("Enter the data : ");

data = sc.nextInt();

ll.addAtEnd(data); // Push the data into the queue

System.out.print("Do you want to add more (y/n) : ");

}while(sc.next().equals("y"));

// Show the queue data : 

System.out.println("Queue : ");

ll.showData();

// Remove the first element out of the queue (FIFO Mechanism)

System.out.println("\nQueue after removing one element out : ");

ll.deleteNode();

ll.showData();

// Show last element of the queue

System.out.print("\nLast Element : ");

ll.showLastElement();

}

}