StateViewModel.java

class StateViewModel extends AndroidViewModel {
    private final ScheduledExecutorService myExecutor;
    private String mData; // This value doesn't change after it is initialized
    private CounterLiveData mCounter = new CounterLiveData(); // This value changes over time

    public StateViewModel(Application context) {
        super(context);
        myExecutor = Executors.newSingleThreadScheduledExecutor();
        myExecutor.scheduleWithFixedDelay(this::recurringTask, 0, 1, TimeUnit.SECONDS);
        Log.d(Tags.viewmodel.name(), "ViewModel constructor: created executor");
    }

    // Counter
    public void recurringTask() {
        long counter = mCounter.get();
        Log.d(Tags.viewmodel.name(), counter % 2 == 0 ? "task: tick" : "task: tock");
        mCounter.set(counter + 1);
    }

    public CounterLiveData getCounter() {
        return mCounter;
    }

    // Data
    public void setData(String mData) {
        this.mData = mData;
    }

    public String getData() {
        if (isDataSet()) {
            Toast.makeText(getApplication(), "Re-using ViewModel", Toast.LENGTH_SHORT).show();
        } else {
            setData(UUID.randomUUID().toString());
            Toast.makeText(getApplication(), "This is a new ViewModel", Toast.LENGTH_SHORT).show();
        }
        return mData;
    }

    public boolean isDataSet() {
        return mData != null;
    }

    @Override
    protected void onCleared() {
        super.onCleared();
        myExecutor.shutdown();
        Log.d(Tags.viewmodel.name(), mCounter.toString());
        Log.d(Tags.viewmodel.name(), "onCleared: lifecycle of activity finished");
    }
}