设计一个储存对象的栈类Stack（可以使用一个ArrayLiist来实现）

import java.util.ArrayList;

public class Stack {
    private ArrayList<Object> list = new ArrayList<>();//一个储存元素（对象）的列表

    public boolean isEmpty() {
        return list.isEmpty();//如果栈为空，则返回true
    }

    public int getSize() {//返回栈中元素个数
        return list.size();
    }

    public Object peek() {//返回栈顶元素而不删除它
        return list.get(list.size() - 1);
    }

    public Object pop() {//返回并删除该栈的栈顶元素
        Object o = list.get(list.size() - 1);
        list.remove(o);
        return o;
    }

    public void push(Object o) {//添加一个新的元素到栈的顶部
        list.add(o);
    }

    @Override
    public String toString() {//重写toString方法
        return "Stack" + list;
    }


}
public class Test {
    public static void main(String[] args) {
        Stack stack = new Stack();
        for (int i = 0; i <20; i++) {
            stack.push(i);
        }
        for (int i=0;i<18;i++){
            System.out.print(stack.pop()+" ");
        }
        stack.push("ok");
        stack.push(2.36);


        System.out.println("\n"+stack.toString());
    }
}
"D:\java 12.0\bin\java.exe" "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2019.2\lib\idea_rt.jar=60880:C:\Program Files\JetBrains\IntelliJ IDEA 2019.2\bin" -Dfile.encoding=UTF-8 -classpath C:\Users\26601\Desktop\library_management_sys-master\untitled15\out\production\untitled15 Test
19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 
Stack[0, 1, ok, 2.56]

Process finished with exit code 0