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 {

    // other code

    private void method1() {
        final SomeObject obj1 = new SomeObject(...);
        final SomeObject obj2 = new SomeObject(...);
        someManager.registerCallback(new SomeCallbackClass() {
            @Override
            public void onEvent() {
                 System.out.println(obj1.getName());
            }
        });
    }
}

Assume that registerCallback saves its parameter somewhere, so that the object of the anonymous subclass will live for a while. Obviously this object has to maintain a reference to obj1 so that onEvent will work if it is called.

But given that the object doesn't use obj2, does it still maintain a reference to obj2, so that obj2 can't be garbage-collected while the object lives? I was under the impression that all visible final (or effectively final) local variables and parameters were captured and thus couldn't be GC'ed as long as the object was alive, but I can't find anything that says one way or the other.

Is it implementation-dependent?

Is there a section in the JLS that answers this? I wasn't able to find the answer there.

Answer 1

The language spec has very little to say about how anonymous classes should capture variables from their enclosing scope.

The only especially relevant section of the language spec that I can find is JLS Sec 8.1.3:

Any local variable, formal parameter, or exception parameter used but not declared in an inner class must either be declared final or be effectively final (§4.12.4), or a compile-time error occurs where the use is attempted.)

(Anonymous classes are inner classes)

It does not specify anything about which variables the anonymous class should capture, or how that capturing should be implemented.

I think it is reasonable to infer from this that implementations need not capture variables that aren't referenced in the inner class; but it doesn't say they can't.