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

ViewModelProvider.java

public <T extends ViewModel> T get(@NonNull Class<T> modelClass) {
    String canonicalName = modelClass.getCanonicalName();
    if (canonicalName == null) {
        throw new IllegalArgumentException("Local and anonymous classes can not be ViewModels");
    }
    return get(DEFAULT_KEY + ":" + canonicalName, modelClass);
}

public <T extends ViewModel> T get(@NonNull String key, @NonNull Class<T> modelClass) {
    ViewModel viewModel = mViewModelStore.get(key);
    if (modelClass.isInstance(viewModel)) {
        return (T) viewModel;
    } else {
        ...
    }
    viewModel = mFactory.create(modelClass);
    mViewModelStore.put(key, viewModel);
    return (T) viewModel;
}