Logging from default interface methods

Question

Salut to all Java gurus!

Since Java8 we can have default implementations in interfaces (yay!). However problem arises when you want to log from default method.

Answer 1

If you don’t want to expose the class LogHolder to the public, don’t make it a member class of the interface. There is no benefit in making it a member class, you don’t even save typing as you have to qualify the field access with the name of the holder class anyway, regardless of whether it is a member class or a class within the same package:

public interface WithTimeout {

    default void onTimeout(Action timedOutAction) {
        LogHolder.LOGGER.info("Action {} time out ignored.", timedOutAction);
    }
}
final class LogHolder { // not public
    static final Logger LOGGER = getLogger(WithTimeout.class);
}