Java - When to Use Foo＜？＞

Heterogenous Tuple of Infinite Size

One example use case of Foo<?> is an implementation of a Tuple of infinite size storing different object types

public class Favorites {
	private Map<Class<?>, Object> favorites = new HashMap<>();

	public <T> void putFavorite(Class<T> type, T instance) {
		Assert.assertNotNull(instance);
		favorites.put(type, instance);
	}

	public <T> T getFavorite(Class<T> type) {
		return type.cast(favorites.get(type));
	}
}