引用传递

序

这块内容网上一搜一大片，但还是自己的理解和亲身测验更靠谱一些。

引用传递1

public class Demo {
    public static void main(String[] args) {
        Person per = new Person("01", "UUUUU");
        changePer(per);
        System.out.println(per);
    }
    private static void changePer(Person per) {
        per.setName("UIASUIAS");
    }
}

结果：
Person{id='01', name='UIASUIAS'}
Process finished with exit code 0

显然，这是引用传递，另外解释一下JVM，方法区存在的是这个person 的描述（也可称之为一个模型），new person()的实例对象存在堆内存中，堆中可以存在多个person的实例。

引用传递2

public class Demo {
    public static void main(String[] args) {
        ArrayList<Person> list = new ArrayList<>();
        Person per = new Person("01", "UUUUU");
        list.add(per);
        System.out.println(JSON.toJSONString(list));
        per.setName("PPPPPPPPp");
        System.out.println(JSON.toJSONString(list));
        change(list);
        System.out.println(JSON.toJSONString(list));
    }
    public static void change(ArrayList<Person> list){
        list.get(0).setName("TTTT");
    }
}

结果：
[{"id":"01","name":"UUUUU"}]
[{"id":"01","name":"PPPPPPPPp"}]
[{"id":"01","name":"TTTT"}]

Process finished with exit code 0

显然2，不仅在list.add（）后修改list中的对象为引用传递，把list当做参数传给方法也为引用传递，list.get(0)还是获得了main方法里person的引用地址

引用传递3

 public static void main(String[] args) {
        ArrayList<Person> list = new ArrayList<>();
        Person per = new Person("01", "UUUUU");
        list.add(per);
        ArrayList<Person> list1 = new ArrayList<>();
        list1.addAll(list);
        System.out.println(JSON.toJSONString(list1));
        per.setName("PPPPPPPPp");
        System.out.println(JSON.toJSONString(list1));
    }

结果：
[{"id":"01","name":"UUUUU"}]
[{"id":"01","name":"PPPPPPPPp"}]

Process finished with exit code 0

显然3，这个也是引用传递