java 实现下压栈的操作(能动态调整数组大小)

import java.util.Iterator;
public class ResizingArrayStack<Item> implements Iterable<Item>
{
  private Item[] a=(Item[]) new Object[1];
  private int N=0;
  public boolean isEmpty() { return N==0;}
  public int size() {return N;}
  private void resize(int max)
  {
    Item[] temp=(Item[]) new Object[max];
    for(int i=0; i<N; i++)
    {
      temp[i]=a[i];
    }
    a=temp;
  }
  public void push(Item item)
  {
    if(N==a.length) resize(2*a.length);
    a[N++]=item;
 
  }
  public Item pop()
  {
    Item item=a[--N];
    a[N]=null;
    if(N>0 && N==a.length/4) resize(a.length/2);
    return item;
  }
  public Iterator<Item> iterator()
  {return new ReverseArrayIterator();}
  private class ReverseArrayItertor implements Iterator<Item>
  {
    private int i=N;
    public boolean hasNext() {return i>0;}
    public Item next() {return a[--i];}
    public void remove() {}
  }
}

package com.atguigu.stack; 
import java.util.Scanner; 
public class ArrayStackDemo {
 public static void main(String[] args) {
 //测试
 ArrayStack stack =new ArrayStack(4);
 String key="";
 boolean loop = true;
 Scanner scanner = new Scanner(System.in);
 
 while(loop) {
  System.out.println("show:表示显示栈");
  System.out.println("exit:退出程序");
  System.out.println("push:表示添加数据到栈（入栈）");
  System.out.println("pop:表示从栈取出数据（出栈）");
  System.out.println("请输入你的选择");
  key = scanner.next();
  switch(key) {
  case "show":
  stack.list();
  break;
  
  case "push":
  System.out.println("请输入一个数");
  int value = scanner.nextInt();
  stack.push(value);
  break;
  
  case "pop":
  try {
   int res = stack.pop();
   System.out.printf("出栈的语句是%d\n", res);
  }catch(Exception e) {
   System.out.println(e.getMessage());
  }
  break;
  
  case "exit":
  scanner.close();
  loop = false;
  break;
  default:
   break;
  }
 }
 System.out.println("程序退出");
 } 
}
 
class ArrayStack{
 private int maxSize;
 private int[] stack;
 private int top = -1; 
 public ArrayStack(int maxSize) {
 this.maxSize=maxSize;
 stack = new int[this.maxSize]; 
 }
 
  //栈满
 public boolean isFull() {
 return top == maxSize -1;
 
 }
  //栈空
 public boolean isEmpty() {
 return top == -1;
 
 }
 //出栈
 public void push(int value) {
 if(isFull()) {
  System.out.println("栈满");
 }
 top++;
 stack[top] =value;
 }
 //出栈
 public int pop() {
 if(isEmpty()) {
  throw new RuntimeException("栈空");
 }
 int value = stack[top];
 top--;
 return value;
 }
 //遍历栈
 public void list() {
 if(isEmpty()) {
  System.out.println("栈空，没有数据");
  return;
 }
 for(int i = top;i>=0;i--) {
  System.out.printf("stack[%d]=%d\n",i,stack[i]);
 }
 }
}