public class SampleActivity extends FragmentActivity {

    @Retain
    Object mObjectToRetain;

    //objects marked with @NonNull and @Retain will be checked for null during save()/restore() calls
    //and if they are null, NullPointerException will be thrown
    @NonNull
    @Retain
    Object mNonNullObjectToRetain;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        BeRetained.onCreate(this);

        if(!BeRetained.restore(this)) {
            //oops, couldn't restore! Looks like it's a first start or app was killed
            mObjectToRetain = new Object();
            mNonNullObjectToRetain = new Object();
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        BeRetained.save(this);
    }
}