1 实验源码

关键方法: updateUser*()

import org.junit.Test;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;

public class MainTest {
    @Test
    public void testModifyInStreamForEachOfList1() {
        ArrayList<User> list = new ArrayList<User>();
        User user = new User();
        user.name = "wahahahhaha";
        list.add(user);
        list.stream().forEach(item -> {
            item.name = "efisgbdfjsb";// 为已设置值的字段 更新 值
            item.age = 4; // 为未设置值的字段 设置 新值
        });
        list.stream().forEach(item -> {
            System.out.println(item);
        });
        //output: name:efisgbdfjsb/tage:4
    }

    @Test
    public void testModifyInStreamForEachOfList2() {
        ArrayList<User> list = new ArrayList<User>();
        User user = new User();
        user.name = "wahahahhaha";
        list.add(user);
        list.stream().forEach(item -> {
            item = updateUserByOldObject(item);
        });
        list.stream().forEach(item -> {
            System.out.println(item);
        });
        //output: name:efisgbdfjsb/tage:4
    }

    @Test
    public void testModifyInStreamForEachOfList3() {
        ArrayList<User> list = new ArrayList<User>();
        User user = new User();
        user.name = "wahahahhaha";
        list.add(user);
        list.stream().forEach(item -> {
            updateUserByOldObject(item);
        });
        list.stream().forEach(item -> {
            System.out.println(item);
        });
        //output: name:efisgbdfjsb/tage:4
    }

    @Test
    public void testModifyInStreamForEachOfList4() {
        ArrayList<User> list = new ArrayList<User>();
        User user = new User();
        user.name = "wahahahhaha";
        list.add(user);
        list.stream().forEach(item -> {
            item = updateUserByNewObject(user);
        });
        list.stream().forEach(item -> {
            System.out.println(item);
        });
        //output: name:wahahahhaha/tage:0
    }

    public User updateUserByOldObject(User user) {//在 旧对象上做修改，然后返回
        user.name = "efisgbdfjsb";// 为已设置值的字段 更新 值
        user.age = 4; // 为未设置值的字段 设置 新值
        return user;
    }

    public User updateUserByNewObject(User user) {//在 new 的新对象上做修改，然后返回
        User newUser = new User();
        newUser.name = "efisgbdfjsb";// 为已设置值的字段 更新 值
        newUser.age = 4; // 为未设置值的字段 设置 新值
        return newUser;
    }
}

class User{
    public String name;
    public int age;

    @Override
    public String toString(){
        return "name:"+name+"/t"+"age:"+age;
    }
}

[Java SE]Java方法的值传递【待续】

原文：https://www.cnblogs.com/johnnyzen/p/13938500.html