在索引处添加到 ArrayList 时出现 IndexOutOfBoundsException [英] IndexOutOfBoundsException when adding to ArrayList at index

问题描述

我得到异常 Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 1, Size: 0 对于下面的代码.但不明白为什么.

I get exception Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 1, Size: 0 for the below code. But couldn't understand why.

public class App {
    public static void main(String[] args) {
        ArrayList<String> s = new ArrayList<>();

        //Set index deliberately as 1 (not zero)
        s.add(1,"Elephant");

        System.out.println(s.size());                
    }
}

更新

我可以让它工作，但我试图理解这些概念，所以我将声明更改为下面但也不起作用.

Update

I can make it work, but I am trying to understand the concepts, so I changed declaration to below but didnt work either.

ArrayList<String> s = new ArrayList<>(10)

推荐答案

ArrayList 索引从 0(零)开始

您的数组列表大小为 0，并且您要在第一个索引处添加 String 元素.如果不在第 0 个索引处添加元素，则无法添加下一个索引位置.这是错误的.

Your array list size is 0, and you are adding String element at 1st index. Without adding element at 0th index you can't add next index positions. Which is wrong.

所以，简单地把它变成

 s.add("Elephant");

或者你也可以

s.add(0,"Elephant");

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