Activity OnDestroy never called?

I am using following code in my ListActivity

// a separate class in project
public class MyActivity extends ListActivity {
    // some common functions here..
}

public class SelectLocation extends MyListActivity {

    public void onCreate(Bundle savedInstance) {
        // here.....
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (adap != null) adap = null;
        if (list != null) list = null;
        System.gc();
    }
}

any one guide me why onDestroy method is not called in my code?

Solution

onDestroy() is called only when the system is low on resources (memory, cpu time, etc) and makes a decision to kill your activity/application or when somebody calls finish() on your activity.

So, to test your code you can make a test button, that will call finish() on your activity.