Question

Memory leak in below example.

1.SpeedHelper.java:

public class SpeedHelper {

    interface Listener {
        void OnSelected(String entry);
    }
    static Listener sListener;

    static void setListener(Listener listener) {
        sListener = listener;
    }
    static Listener getListener() {
        return sListener;
    }
    static void clearListener() {
        sListener = null;
    }
}

2.CallSpeed.java

public class CallSpeed {

    protected void speed() {
        SpeedHelper.Listener litener = SpeedHelper.getListener();
        if (litener != null) {
            litener.OnSelected("mEntry");
        }
    }
}

3.MainActivity.java

public class MainActivity extends Activity {

    private CallSpeed callspeed;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        SpeedHelper.setListener(mCallSpeedListener);
        callspeed = new CallSpeed();
        callspeed.speed();
    }
    private SpeedHelper.Listener mCallSpeedListener = new SpeedHelper.Listener() {

        @Override
        public void OnSelected(String entry) {
            Toast.makeText(getApplicationContext(), entry, Toast.LENGTH_SHORT).show();
        }
    };
    @Override
    protected void onDestroy() {
        // TODO Auto-generated method stub
        super.onDestroy();
        SpeedHelper.clearListener();
    }
}

How to avoid Memory leak for “sListener”?

Answer 1

Your problem lies in the following non-static enclosed anonymous class in association with the static field sListener:

private SpeedHelper.Listener mCallSpeedListener = new SpeedHelper.Listener() {

        @Override
        public void OnSelected(String entry) {
            Toast.makeText(getApplicationContext(), entry, Toast.LENGTH_SHORT).show();
        }
    };

Because this is a non-static enclosed class, it contains a reference to its outer class, MainActivity. This hidden reference blocks the release of the MainActivity class by the GC because the object mCallSpeedListener – which contains the hidden reference – get stored in the static field sListener with the instruction SpeedHelper.setListener(mCallSpeedListener);. Therefore, the MainActivity object is never collected, its onDestroy function is never called and everything remains in memory; out of reach of the GC. Using static fields is a door wide open to memory leaks and the presence of hidden references in enclosed classes (anonymous or not) amplifies this problem.

In your case, you will have to either remove the static field sListener or change the anonymous class to an ordinary class; one without the hidden reference to its outer MainActivity class or make a direct call to clearListener in another callback of the activity when it is terminated.