Queue implementation in Java

Question

This is my Queue implementation in Java. Would appreciate a review of the code.

import java.util.Iterator;
public class Queue<T>implements Iterable<T> {
 private Node first, last;
 private int size;
 @Override
 public QueueIterator iterator() {
 return new QueueIterator();
 }
 private class QueueIterator implements Iterator<T>{
 private Node current = first;
 public boolean hasNext(){
 return current != null;
 }
 public T next(){
 T item = current.data;
 current = current.next;
 return item;
 }
 }
 private class Node{
 Node(T data){
 this.data = data;
 this.next = null;
 }
 T data;
 Node next;
 }
 public Queue(){
 first = last = null;
 size = 0;
 }
 public void enqueue(T item){
 Node p = new Node(item);
 if(first == null){
 first = last = p;
 size++;
 return;
 }
 last.next = p;
 last = p;
 size++;
 }
 public T dequeue(){
 Node p = first;
 try{
 first = first.next;
 size--;
 }catch(Exception e){
 System.out.println("Dequeing an empty queue :" + e);
 }
 return p.data;
 }
 public boolean isEmpty(){
 return last == null;
 }
}

Answer 1

• Bug

  dequeue doesn't set last to null when the queue becomes empty. On the other hand, isEmpty relies on last being null.

• enqueue should be streamlined to

   if (first == null) {
   first = p;
   } else {
   last->next = p;
   }
   last = p;
   size++;
  

  to clearly state common vs different actions.