Referring instance variable in anonymous inner class

Question

class MyClass1 {

    int x = 10;

    public static void main(String[] args) {
        MyClass1 obj = new MyClass1();
        obj.execute();
    }

    private  void execute() {
        Thread t = new Thread(new Runnable(){
            @Override
            public void run() {
                System.out.println(this);
                System.out.println(MyClass1.this.x);
            }
        });
        t.start();
    }

}

Here this refers to an object of anonymous inner class. That is why this.x does not work. But how can we use this to refer to MyClass1 object? Please explain. When we do Sysout(this), it prints out com.java.MyClass1$1@3cd7c2ce where $ specify inner class object. I am not clear on this.

@HovercraftFullOfEels that shouldn´t work for a class member variable within the static main or? — SomeJavaGuy, May 24 '17 at 14:32
There is no MyClass1.thiss within the static world. User you need to create a MyClass1 instance first. — Hovercraft Full Of Eels, May 24 '17 at 14:33
https://stackoverflow.com/questions/11664522/why-cant-we-use-this-keyword-in-a-static-method — masterG, May 24 '17 at 14:38
I would define the class as `class MyClass1 implements Runnable`, then define the `run()` method in the `MyClass1` body and start the thread with `new Thread(this).start()` (or directly in the main function with `new Thread(obj).start()`). — Oneiros, May 24 '17 at 15:20

score 5 · Answer 1 · answered May 24 '17 at 14:33

5

You can't use this keyword in a static method because this points to an instance of the class and in the static method, you don't have an instance.

answered May 24 '17 at 14:33

Itzik Shachar

744
5
16

score 3 · Answer 2 · edited May 24 '17 at 14:35

3

The method in which you are creating the anonymous inner class is not an instance method but a static method.

Also, the syntax is MyClass1.this.x, not this.x.

To make it work, rewrite it like this:

class MyClass1 {
    int x= 10;
    public static void main(String[] args) {
        new MyClass1().main();
    }

    private void main() {
        Thread t= new Thread(new Runnable(){

            @Override
            public void run() {
                System.out.println(this);

                System.out.println(MyClass1.this.x);
            }
        });
        t.start();
    }
}

edited May 24 '17 at 14:35

dumbPotato21

5,669
5
21
34

answered May 24 '17 at 14:34

Rolf Schäuble

690
4
15

I understood that here this refers to object of anonymous inner class. So if it is an instance method, still this refers to anonymous inner class , then how can you refer it as MyClass1.this.x? I mean how can we use this to refer to MyClass1 obj? I am still not clear on this. – Payal Bansal May 24 '17 at 14:40
In this example, an instance method of MyClass1 creates an inner class. The inner class gets a 'hidden' field of type `MyClass1`, to which you can refer in the code by `MyClass1.this`. – Rolf Schäuble May 24 '17 at 14:46

Referring instance variable in anonymous inner class

2 Answers2