public class Queue_byLinkedList {

static class Node{

int data;

Node next;

Node(int data){

this.data = data;

next = null;

}

}

static class Queue{

static Node head = null;

static Node tail = null;

public static boolean isEmpty(){

return head == null && tail == null;

}

public static void add(int data){

Node newNode = new Node(data);

if(tail == null) {

tail=head=newNode;

return;

}

tail.next = newNode;

tail = newNode; // assigning newNode as value to tail

}

public static int remove(){

if (isEmpty()){

System.out.println("empty queue");

return -1;

}

int front = head.data;

if(head == tail) tail = null;

head = head.next;

return front;

}

public static int peek(){

if (isEmpty()){

System.out.println("empty queue");

return -1;

}

return head.data;

}

}

public static void main(String[] args) {

Queue q = new Queue();

q.add(0);

q.add(1);

q.add(2);

q.add(3);

//q.remove();

while(!q.isEmpty()){

System.out.println(q.peek());

q.remove();

}

}

}