方法传参List类型没有被赋值

问题：方法传参List，并对变量赋值，但是在主方法使用List时，没有赋值成功？

原因：1、是否是方法内的局部变量；2、方法是否已经结束，如果结束，JVM回收结束方法内的局部变量；

解决方案：1、使用addAll()；2、使用add()；3、使用方法的返回值；

测试代码：

package com.zc.es.util;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * @description
 * @Author zc
 * @Datetime 2022/7/2 11:35
 */
public class TestUtil {

    public static void main(String[] args) {
        // 【错误】result集合为空
        List<Integer> result1 = new ArrayList<>();
        list1(result1);
        System.out.println("result1.hashCode= "+result1.hashCode());
        System.out.println("result1= "+result1);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        // 【错误】result集合为空

        // 【正确】result集合有值
        List<Integer> result2 = new ArrayList<>();
        list2(result2);
        System.out.println("result2.hashCode= "+result2.hashCode());
        System.out.println("result2= "+result2);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        // 【正确】result集合有值

        // 【正确】result集合有值
        List<Integer> result3 = new ArrayList<>();
        list3(result3);
        System.out.println("result3.hashCode= "+result3.hashCode());
        System.out.println("result3= "+result3);
        result3.remove(1);
        System.out.println("移除一个元素result3= "+result3);
        System.out.println("result3.hashCode= "+result3.hashCode());
        System.out.println("result3= "+result3);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        // 【正确】result集合有值

        // 【正确】result集合有值
        List<Integer> result4 = list4();
        System.out.println("result4.hashCode= "+result4.hashCode());
        System.out.println("result4= "+result4);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        // 【正确】result集合有值
    }
    /**  */
    private static void list1(List<Integer> result){
        List<Integer> list = Arrays.asList(1,2,3);
        result = list;
        System.out.println("list.hashCode= "+list.hashCode());
    }
    private static void list2(List<Integer> result){
        List<Integer> list = Arrays.asList(1,2);
        result.addAll(list);
        System.out.println("list.hashCode= "+list.hashCode());
    }
    private static void list3(List<Integer> result){
        List<Integer> list = Arrays.asList(1,2,3);
        list.forEach(x-> result.add(x));
        System.out.println("list.hashCode= "+list.hashCode());
    }
    private static List<Integer> list4(){
        List<Integer> list = Arrays.asList(1,2,3,4);
        System.out.println("list.hashCode= "+list.hashCode());
        return list;
    }


}

输入结果：

list.hashCode= 30817
result1.hashCode= 1
result1= []
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
list.hashCode= 994
result2.hashCode= 994
result2= [1, 2]
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
list.hashCode= 30817
result3.hashCode= 30817
result3= [1, 2, 3]
移除一个元素result3= [1, 3]
result3.hashCode= 995
result3= [1, 3]
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
list.hashCode= 955331
result4.hashCode= 955331
result4= [1, 2, 3, 4]
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Process finished with exit code 0