Error implementing a Java or Groovy generic interface

Hello.

I have an issue creating a Groovy class implementing an interface coded in Java with Generics:
Here is the code:

/* Java interface */
public interface Entity<T> {
	T getId();	
}

/* Groovy class */
class Car implements Entity<Long> {
      Long id;
}

Car groovy class has a Long getId() method already, but it doesn't recognize it's enough to implement the interface method:
"Can't have an abstract method in a non-abstract class. The class 'Car' must be declared abstract or the method 'java.lang.Object getId()' must be implemented."

The same happens when the interface is coded in Groovy instead of Java.

I believe it's an important thing to support.

I am using Groovy 1.7.3.

Thank you.