使用一个数组实现栈

public class MyStack {    private Object[] stack;    private int size;//元素的个数    //初始化数组的大小    public MyStack(int length){        stack=new Object[length];    }    //元素的个数    public int size(){        return size;    }    //动态扩展数组    public void ensureCapacity(){        if(size()==stack.length){            Object[] newStack=new Object[size()*3/2+1];            System.arraycopy(stack,0,newStack,0,size());            stack=newStack;        }    }    //判断栈是否已满    public boolean isFull(){        return size>=stack.length;    }    //判断栈是否为空    public boolean isEmpty(){        return size==0;    }    //入栈    public void push(Object obj){        size++;        ensureCapacity();        stack[size-1]=obj;    }    //出栈    public Object pop(){        Object obj=stack[--size];        stack[size]=null;        return obj;    }    public static void main(String[] args) {        MyStack myStack=new MyStack(4);        String[] s={"a","b","c","d"};        for (int i = 0; i <4; i++) {            myStack.push(s[i]);        }        while(!myStack.isEmpty()){            System.out.print(myStack.pop()+" ");        }    }}