"Type safe" UUIDs?

Question

We use make heavy usage of java.util.UUID in our projects to identify ojbects and do operations on them like in this interface:

List<UUID> searchPerson(String text);
Person fetchPerson(UUID personUUID);

List<UUID> searchAdress(String text);
Person fetchAdress(UUID adressUUID);

But what can happen now, and is a source of Runtime errors, is that a developer accidently passes a personUUID to the fetchAdress method, which should not happen.

Is there any way to make this kind of "type safe" so hat he can't pass the fetchAdress method a personUUID? Maybe there is a way to do this using generics?

Answer 1

Build a class that includes UUID functionality by composition, and then subclass it for each individual "type" of UUID you need.

If you don't need/want the full UUID API on your subclasses, you could be extra lazy and just wrap it. Something like this:

public class MyUUID {
    private UUID uuid;
    public MyUUID() {
         uuid = UUID.randomUUID();
    }

    public UUID getUUID() {
        return uuid;
    }
}

public class PersonUUID extends MyUUID { }
public class AddressUUID extends MyUUID { }

If manually unwrapping to get the UUID object out annoys you, just implement the full UUID API on MyUUID and delegate each call to the uuid member.