Java的Map操作与Golang的Map操作的区别

Java版本 

import java.util.HashMap;
import java.util.Map;

public class Main {
    public static String KEY="TEST-KEY";
    
    public static void main(String[] args) {

        Map<String,Filed> map= new HashMap<>();

        map.put(KEY,new Filed(100));

        Filed v = map.get(KEY);
        v.setCount(200);

        System.out.println(map.get(KEY).getCount());
    }
}

class Filed{
    private int count;


    public Filed(int count) {
        this.count = count;
    }

    public void setCount(int count) {
        this.count = count;
    }

    public int getCount() {
        return count;
    }
}

输出结果为: 200

 

Golang版本

 

package main

import "fmt"

const KEY  = "TEST-KEY"

type Filed struct {
	Count int
}

func main() {

	fileds := make(map[string]Filed)

	fileds[KEY] = Filed{Count: 100}

	filed := fileds[KEY]
	filed.Count = 200

	fmt.Println(fileds[KEY].Count)
}

输出结果为: 100

原因是这里从map中拿到的对象是局部变量，对局部变量的修改不影响map中对应key的值

 

与java相同功能的代码

package main

import "fmt"

const KEY  = "TEST-KEY"

type Filed struct {
	Count int
}

func main() {

	fileds := make(map[string]*Filed)

	fileds[KEY] = &Filed{Count: 100}

	filed := fileds[KEY]
	filed.Count = 200

	fmt.Println(fileds[KEY].Count)
}

输出结果为: 200

这里从map中拿到的对象是一个指针，对指针的修改影响map中对应key的值