The third limitation is that, if the class were to be extended (e.g., by making the constructor protected—this is risky but feasible), the subclass must provide its own re-implementation of all factory methods with exactly the same signatures.
A terceira limitación é que se estendemos a clase, por exemplo facendo o construtor protexido, a subclase pode prover as súas propias reimplementacións dos métodos factorías coas mesmas firmas.