浅析Java 对象引用和对象本身

import com.alibaba.fastjson.JSONObject;
import java.util.ArrayList;
import java.util.List;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * @author gzh
 * @createTime 2020/8/25 8:41 AM
 */
public class Test {
 private static final Logger log = LoggerFactory.getLogger(Test.class);

 public static void main(String[] args) {
  //
  List<User> userList = new ArrayList<User>();
  User user1 = new User();
  user1.setName("gzh1");
  userList.add(user1);

  User user2 = new User();
  user2.setName("gzh2");
  userList.add(user2);

  log.info(JSONObject.toJSONString(userList));

  //
//  for (User user: userList) { //这里的list元素最终是旧值，因为没有被新的对象本身直接赋值
//   log.info(JSONObject.toJSONString(user));
//   User user3 = new User();
//   user3.setName("gzh3");
//
//   user = user3;
//   log.info(JSONObject.toJSONString(user));
//  }

//  for (int i = 0; i < userList.size(); i++) { //这里的list元素最终是新值，因为被新的对象本身直接赋值
//   //
//   User user = userList.get(i);
//
//   //
//   log.info(JSONObject.toJSONString(user));
//   User user3 = new User();
//   user3.setName("gzh3");
//   user = user3;
//
//   //
//   log.info(JSONObject.toJSONString(user));
//   userList.set(i,user);
//  }

  for (int i = 0; i < userList.size(); i++) { //同上：这里的list元素最终是新值，因为被新的对象本身直接赋值
   //
   log.info(JSONObject.toJSONString(userList.get(i)));

   //
   User user3 = new User();
   user3.setName("gzh3");

   //
   userList.set(i,user3);
   log.info(JSONObject.toJSONString(userList.get(i)));
  }

  //
  log.info(JSONObject.toJSONString(userList));
 }
}

import com.alibaba.fastjson.JSONObject;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * @author gzh
 * @createTime 2020/8/25 8:41 AM
 */
public class Test2 {
 private static final Logger log = LoggerFactory.getLogger(Test2.class);

 public static void main(String[] args) {
  User user = new User();
  user.setName("gzh1");

  log.info("调用方法之前:{}",JSONObject.toJSONString(user));
  updateUser2(user);
  log.info("调用方法之后:{}",JSONObject.toJSONString(user));
 }

 private static void updateUser(User user) {
  //
  log.info(JSONObject.toJSONString(user));

  //
  User user2 = new User();
  user2.setName("gzh2");

  user = user2;

  //
  log.info(JSONObject.toJSONString(user));
 }

 private static void updateUser2(User user) {
  //
  log.info(JSONObject.toJSONString(user));

  user.setName("gzh2");

  //
  log.info(JSONObject.toJSONString(user));
 }
}