QUEUE

package algorithm.queue;

public class Queue {

 private Node head = null;
 private Node tail = head;

 private int size = 0;

 public void enQueue(int number) {
  
  Node queue = new Node();
  queue.number = number;
  
  if (head == null) {
   head = queue;
   tail = head;
  } else {
   tail.next = queue;
   tail = queue;
  }
  size++;
 }

 public int deQueue() throws QueueException {

  if (!isEmpty()) {
   int temp = head.number;
   head = head.next;
   size--;
   return temp;
  }else{
   throw new QueueException("no data.size is 0");
  }
 }

 public boolean isEmpty() {
  if (size == 0) {
   return true;
  } else {
   return false;
  }
 }
 
 public int size(){
  return this.size;
 }
}
-----------------

package algorithm.queue;

public class Node {

 int number;
 
 Node next = null; 
}