Android - WeakReference.get() and NullPointerException

      Just came across a less reproducible NPE around WeakReferences and no wonder this wasn't caught in a code review. In this case, the back end logic held a WeakReference on a ListView's adapter and the idea is to update the ListView only when its necessary. The code was very simple and is often overlooked.

            if (mAdapter.get() != null) {
                mAdapter.get().notifyDataSetChanged();
            } 

 And this worked fine except for a crash once in a while. Basically, the WeakReference was holding on to the object in the check but not when it was being used to update the adapter. So the object was basically garbage collected. Thats a tiny window for a race and yet the GC found its way. So just to demonstrate, how about repeated attempts?

        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.gc();
                }
            }
        });

            if (mAdapter.get() != null) {
                while (true) {
                    Log.e("GC", "Actual object is [" + mAdapter.get() + "]");
                }
            }


  A thread is launched just to trigger garbage collection once a second and that basically illustrates the problem.