java Arrays.asList 返回什么与普通 ArrayList 区别介绍

import java.util.Arrays;
import java.util.List;
import java.util.ArrayList;
public class Main {
    public static void main(String[] args) {
        // 1. 创建一个原始数组
        String[] originalArray = {"A", "B", "C"};
        // 2. 使用 Arrays.asList 得到一个 List
        List<String> asList = Arrays.asList(originalArray);
        System.out.println("asList: " + asList); // 输出: [A, B, C]
        // 3. 创建一个普通的 ArrayList
        List<String> realArrayList = new ArrayList<>(Arrays.asList(originalArray));
        System.out.println("realArrayList: " + realArrayList); // 输出: [A, B, C]
        // --- 测试修改元素 (两者都支持) ---
        asList.set(0, "A_Modified");
        realArrayList.set(0, "A_Modified");
        System.out.println("After set(0):");
        System.out.println("asList: " + asList); // 输出: [A_Modified, B, C]
        System.out.println("realArrayList: " + realArrayList); // 输出: [A_Modified, B, C]
        System.out.println("originalArray: " + Arrays.toString(originalArray)); 
        // 关键！原数组也被修改了: [A_Modified, B, C]
        // 这说明 asList 和 originalArray 共享底层数据
        // --- 测试添加元素 (关键区别) ---
        try {
            realArrayList.add("D"); // 成功
            System.out.println("realArrayList after add: " + realArrayList); // [A_Modified, B, C, D]
        } catch (Exception e) {
            System.out.println("realArrayList add failed: " + e);
        }
        try {
            asList.add("D"); // 失败！抛出异常
        } catch (Exception e) {
            System.out.println("asList add failed: " + e); 
            // 输出: java.lang.UnsupportedOperationException
        }
        // --- 测试删除元素 (关键区别) ---
        try {
            realArrayList.remove(0); // 成功
            System.out.println("realArrayList after remove: " + realArrayList); // [B, C, D]
        } catch (Exception e) {
            System.out.println("realArrayList remove failed: " + e);
        }
        try {
            asList.remove(0); // 失败！抛出异常
        } catch (Exception e) {
            System.out.println("asList remove failed: " + e);
            // 输出: java.lang.UnsupportedOperationException
        }
    }
}