Understanding Weak References

Question

Consider I have a class structure similar to this

class Outer extends Activity {

    Map<String, String> outerMap;

    public Map getSampleMap() {
        return sampleMap;
    }

    static class Inner {
        Map<String, String> innerMap;

        Inner(Outer outer) {
            /* Weak ref to outer class object */
            WeakReference weakref = new WeakReference<Outer>(outer);
            /* reference to the outer map using the weak ref */
            innerMap = weakref.get().getSampleMap();
        }

        void doSomething() {
            // Operations on the innerMap
        }

    }
}

Now in the above code structure

1. Is innerMap hold a strong reference to the outerMap ?
2. If I were to pass the innerMap in a callback such that it outlives the Outer Class (perhaps config changes) would it leak ?
3. Will the outer class object be GC'ed ?

Can someone point me to a good source for reference.

Answer 1

1. No. innerMap is a strong reference to the same object referenced by outer.outerMap. Initializing it via a weak reference to outer does not change that.
2. No. The object referenced by innerMap will be eligible for GC when there cease to be any live, strong references to it. That it was once referenced by an instance variable of some class that has since been GC'ed makes no difference.
3. The existence outside outer of another reference to the same object referenced by outer.outerMap does not inherently prevent the object referenced by outer from itself being GC'ed.

As for resources, you could try

• Understanding weak references, or
• the API docs