自己实现栈

package 栈与队列上;

public class MiniStack {
	private int size;							//size是栈顶指针
	private Object[] array = new Object[4];		//Java不能初始化泛型数组，如果需要，则要使用Java反射实现
	/**
	 * 判断数组是否为空
	 * @return
	 */
	public boolean isEmpty() {
		return size == 0 ? true : false;
	}
	/**
	 * 获取栈的大小
	 * @return
	 */
	public int size() {
		return size;
	}
	/**
	 * 数组扩容
	 */
	public void expandCapacity() {
		Object[] newArray = new Object[size * 2];		//扩容为原数组的2倍
		System.arraycopy(array, 0, newArray, 0, size);	//数组复制
		array = newArray;								//指向新的数组，原来的数组被垃圾回收器回收掉
	}
	/**
	 * push操作
	 * @param t
	 */
	public void push(Object t) {
		array[size] = t;		
		size++;					//栈顶指针
		if (size == array.length) {
			expandCapacity();
		}
	}
	/**
	 * 返回栈顶元素
	 * @return
	 */
	public Object peek() {
		if (isEmpty()) {
			return null;
		} else {
			return array[size - 1];
		}
	}
	/**
	 * 弹栈操作
	 * @return
	 */
	public Object pop() {
		if (isEmpty()) {
			return null;
		} else {
			Object t = peek();
			array[size - 1] = null;		//防止内存泄露
			size--;
			return t;
		}
	}
	
	public static void main(String[] args) {
		MiniStack stack = new MiniStack();
		stack.push(1);
		stack.push(2);
		stack.push(3);
		System.out.println("stack is empty ? It`s " + stack.isEmpty());
		System.out.println("stack`s size "+stack.size);
		while (!stack.isEmpty()) {
			System.out.println("pop " + stack.pop());
		}
		System.out.println("stack is empty ? It`s " + stack.isEmpty());
		System.out.println("stack`s size "+stack.size);
	}
}