[CC150][3.5] Implement a MyQueue class which implements a queue using two stacks

MyQueue.java

import java.util.Stack;

public class MyQueue<T> {
	private Stack<T> pushStack;
	private Stack<T> popStack;
	
	public MyQueue() {
		pushStack = new Stack<T>();
		popStack = new Stack<T>();
	}
	
	public void enqueue(T item) {       // push element into pushStack
		pushStack.push(item);           // push() : O(1)
	}
	
	public T dequeue() {                // if popStack is not empty, pop() from popStack
		if (popStack.isEmpty()) {       // else, push all elements in pushStack into popStack, then pop one item
			if (pushStack.isEmpty())    // pop() : average O(1)
				return null;
			else {
				while (!pushStack.isEmpty())
					popStack.add(pushStack.pop());
			}
		}
		return popStack.pop();
	}

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		MyQueue<Integer> test = new MyQueue<Integer>();
		for (int i = 0; i < 10; i++)
			test.enqueue(i);
		for (int i = 0; i < 5; i++)
			System.out.println(test.dequeue());
		for (int i = 10; i < 15; i++)
			test.enqueue(i);
		for (int i = 0; i < 10; i++)
			System.out.println(test.dequeue());
	}

}