JAVA实现栈

package datastruct;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * 用单链表实现栈，头插法
 * @author Wee bing
 * @param <Item>
 */
public class MyStack<Item> implements Iterable<Item> {
	private Node<Item> head;//头节点
	private int n;//元素个数

	@SuppressWarnings("hiding")
	private class Node<Item> {
		private Item item;
		private Node<Item> next;
		
		private Node(Item item) {
			this.item = item;
		}
	}
	
	public MyStack() {
		head = null;
	}
	
	//栈中元素的个数
	public int size() {
		return n;
	}
	
	//栈是否为空
	public boolean isEmpty() {
		return n == 0;
	}
	
	//入栈
	public void push(Item item) {
		if (item == null) throw new NullPointerException();
		Node<Item> oldHead = head;
		head = new Node<Item>(item);
		head.next = oldHead;
		n++;
	}
	
	//偷瞄栈顶元素
	public Item peek() {
		if (isEmpty()) throw new NoSuchElementException();
		return head.item;
	}
	
	//出栈
	public Item pop() {
		if (isEmpty())	throw new NullPointerException();
		Item item = head.item;
		head = head.next;
		n--;
		return item;
	}
	
	//元素迭代
	@Override
	public Iterator<Item> iterator() {
		// TODO Auto-generated method stub
		return new MyIterator<Item>(head);
	}
	
	@SuppressWarnings("hiding")
	private class MyIterator<Item> implements Iterator<Item> {
		private Node<Item> cur;
		
		private MyIterator(Node<Item> head) {
			this.cur = head;
		}
		
		@Override
		public boolean hasNext() {
			// TODO Auto-generated method stub
			return cur != null;
		}
		
		public Item next() {
			Item item = cur.item;
			cur = cur.next;
			return item;
		}
	}
	
	//测试
	public static void main(String[] args) {
		MyStack<Integer> ms = new MyStack<Integer>();
		ms.push(8);
		ms.push(5);
		ms.push(11);
		ms.push(100);
		ms.push(50);
		ms.push(70);
		ms.push(77);
		ms.push(200);
		System.out.println(ms.size());
		System.out.println(ms.pop());
		System.out.println(ms.size());
		System.out.println(ms.pop());
		System.out.println(ms.size());
		System.out.println("--------------------------");
		Iterator<Integer> arr = ms.iterator();
		while (arr.hasNext()) {
			System.out.println(arr.next());
		}
		System.out.println(ms.size());
		System.out.println(ms.peek());
	}
}