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];
     }
 }