Used to identify when the app goes to foreground or background

AppTransitionStatus.java

public final class AppTransitionStatus implements Application.ActivityLifecycleCallbacks {

    private static final long MAX_BACKGROUND_TIME = 2000;
    private Timer timer;
    private TimerTask task;
    private boolean isBackground = true;

    private final Transition transition;

    public AppTransitionStatus(@NonNull Transition transition) {
        this.transition = transition;
    }

    @Override
    public void onActivityPaused(Activity activity) {
        timer = new Timer();
        task = new TimerTask() {
            public void run() {
                isBackground = true;
                goToBackground();
            }
        };
        timer.schedule(task, MAX_BACKGROUND_TIME);
    }

    @Override
    public void onActivityResumed(Activity activity) {
        if (isBackground) {
            goToForeground();
        }
        stopTimer();
        isBackground = false;
    }

    private void stopTimer() {
        if (task != null) task.cancel();
        if (timer != null) timer.cancel();
    }

    private void goToForeground() {
        transition.appToForeground();
    }

    private void goToBackground() {
        transition.appToBackground();
    }

    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
        // unused but required to implement ActivityLifecycleCallbacks
    }

    @Override
    public void onActivityStarted(Activity activity) {
        // unused but required to implement ActivityLifecycleCallbacks
    }

    @Override
    public void onActivityStopped(Activity activity) {
        // unused but required to implement ActivityLifecycleCallbacks
    }

    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
        // unused but required to implement ActivityLifecycleCallbacks
    }

    @Override
    public void onActivityDestroyed(Activity activity) {
        // unused but required to implement ActivityLifecycleCallbacks
    }

    public interface Transition {
        void appToForeground();
        void appToBackground();
    }
}

MyApplication.java

public class MyApplication extends Application {
 
    @Override
    public void onCreate() {
        super.onCreate();
        registerActivityLifecycleCallbacks(new AppTransitionStatus(new Transition() {
          @Override
          public void appToForeground() {
              Log.d("Transition", "App in Foreground");
          }

          @Override
          public void appToBackground() {
              Log.d("Transition", "App in Background");
          }
      }));
    }
}

The above piece of code is inspired by https://stackoverflow.com/a/15573121/4747587

please set default value of isBackground to true, appToForeground() is not getting called the first time.

You no longer need to do all this. There is an easier way: https://gist.github.com/thsaravana/d585caa69f9eae876123d36c5c0e095f