在arraylist中使用什么来代替charAt

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        String str = "Hello World";
        ArrayList<Character> charList = new ArrayList<>();

        // 将字符串转换为字符数组
        char[] charArray = str.toCharArray();

        // 将字符数组中的字符添加到ArrayList中
        for (char c : charArray) {
            charList.add(c);
        }

        // 访问特定位置的字符
        char firstChar = charList.get(0);
        char lastChar = charList.get(charList.size() - 1);

        System.out.println("First character: " + firstChar);
        System.out.println("Last character: " + lastChar);
    }
}

First character: H
Last character: d