How ViewModelStore works for https://medium.com/@josep.rodriguez/internals-of-android-architecture-components-part-i-the-viewmodel-d893e362a0d9

ViewModelStore.java

final void put(String key, ViewModel viewModel) {
    ViewModel oldViewModel = mMap.get(key);
    if (oldViewModel != null) {
        oldViewModel.onCleared();
    }
    mMap.put(key, viewModel);
}

final ViewModel get(String key) {
    return mMap.get(key);
}