Stack的实现

public class MyStack<AnyType> {
    private AnyType [] theItems;
    private final int DEFAULT_CAPACITY = 100;
    private int top;


    public MyStack(){ //构造函数，生成空表
        clear();
    }

    public void clear(){ //归为默认(清空)
        top = 0;
        ensureCapacity(DEFAULT_CAPACITY);
    }

    public void ensureCapacity(int newCapacity ){ //重置表的容量
        AnyType [] oldItems = theItems;
        theItems = (AnyType []) new Object[newCapacity];//****重新分配空间 注意使用强制转换的方式进行定义
        for (int i = 0 ; i < top; i++){
            theItems[i] = oldItems[i];
        }
    }

    public boolean isEmpty(){  //判断是否为空
        return top == 0;
    }

    public boolean push( AnyType newVal){//末尾添加元素
        if(theItems.length == top)
            ensureCapacity(top * 2 + 1);
        theItems[top++] = newVal;
        return true;
    }

    public AnyType pop(){
        if(top == 0)
            throw new NoSuchElementException();
        return theItems[--top];
    }
}