public class Queue {

private Node front;

private Node back;

private int size;

private class Node{

private int data;

private Node next;

Node(int data){

this.data = data;

}

}

public Queue() {

front = null;

back = null;

}

public void enqueue(int data){

Node fNode = front;

Node newNode = new Node(data);

if(front == null){

front = newNode;

back = newNode;

front.next = null;

}

else{

while(fNode.next != null){

fNode = fNode.next;

}

fNode.next = newNode;

back = newNode;

}

size += 1;

}

public Node dequeue(){

Node nNode;

Node dNode;

if(size != 0){

dNode = front;

nNode = front.next;

front = null;

front = nNode;

size -= 1;

return dNode;

}

else{

System.out.println("There is no data in queue.");

return null;

}

}

public void printQueue(){

Node cNode = front;

for(int i=0; i < size; i++){

System.out.print(cNode.data + " ");

if(cNode != back){

cNode = cNode.next;

}

}

System.out.println("");

}

public boolean isEmpty(){

return front == null? true: false;

}

}