Are all final variables captured by anonymous classes?

Question

I thought I knew the answer to this, but I can\'t find any confirmation after an hour or so of searching.

In this code:

public class Outer {

    // othe         


        

Answer 1

Only obj1 is captured.

Logically, the anonymous class is implemented as a normal class something like this:

class Anonymous1 extends SomeCallbackClass {
    private final Outer _outer;
    private final SomeObject obj1;
    Anonymous1(Outer _outer, SomeObject obj1) {
        this._outer = _outer;
        this.obj1 = obj1;
    }
    @Override
    public void onEvent() {
         System.out.println(this.obj1.getName());
    }
});

^{Note that an anonymous class is always an inner class, so it will always maintain a reference to the outer class, even if it doesn't need it. I don't know if later versions of the compiler have optimized that away, but I don't think so. It is a potential cause of memory leaks.}

The use of it becomes:

someManager.registerCallback(new Anonymous1(this, obj1));

As you can see, the reference value of obj1 is copied (pass-by-value).

There is technically no reason for obj1 to be final, whether declared final or effectively final (Java 8+), except that if it wasn't and you change the value, the copy wouldn't change, causing bugs because you expected the value to change, given that the copying is a hidden action. To prevent programmer confusion, they decided that obj1 must be final, so you can never become confused about that behavior.