动态数组实现下压栈

import java.util.Iterator;

/**
 * 动态数组实现下压栈
 * 成员变量：容器数组arr，元素个数count
 * 私有方法：调整数组大小resize()
 * 公开方法：添加元素push()、删除元素pop()、获取大小size()、判断是否为空isEmpty()
 * 要求：实现泛型、迭代器、
 */
public class ArrayStack<Item> implements Iterable<Item> {
    private Item[] arr;
    private int count;

    public ArrayStack() {
        arr = (Item[])new Object[5];
        count = 0;
    }
    public ArrayStack(int n) {
        arr = (Item[])new Object[n];
        count = 0;
    }

    private void resize(int size){
        Item[] temp =  (Item[])new Object[size];
        for(int i=0;i<arr.length;i++){
            temp[i]=arr[i];
        }
        arr = temp;
    }
    public void push(Item e){
        if(arr.length == count){
            resize(2*arr.length);
        }
        arr[count]=e;
        count++;
    }

    public Item pop(){
        if(count==0) return null;
        Item temp = arr[count-1];
        arr[count-1]=null;
        count--;
        if(count<arr.length/2){
            resize(arr.length/2);
        }
        return temp;
    }

    public int size(){
        return count;
    }

    public boolean isEmpty(){
        if(count==0) return true;
        return false;
    }

    @Override
    public Iterator<Item> iterator() {
        return new Iterator<Item>() {
            int i=count-1;
            @Override
            public boolean hasNext() {
                if(i>=0) return true;
                return false;
            }

            @Override
            public Item next() {
                return arr[i--];
            }
        };
    }
}

/**
 * 测试案例
 */
public class TestCase {
    public static void main(String[] args) {
        ArrayStack<Integer> integers = new ArrayStack<>();
        integers.push(1);
        integers.push(2);
        integers.push(3);
        integers.push(4);
        integers.push(5);
        System.out.println(integers.pop());
        System.out.println(integers.size());
        System.out.println(integers.isEmpty());
        System.out.println("======================");
        for(Integer e :integers){
            System.out.println(e);
        }
    }
}

//结果
5
4
false
======================
4
3
2
1