Is there an n: 1 observer with generics in java? (observer pattern)

Question

I would like to hear your opinion on the use of the observer pattern.

My goal is to implement one specific observer class that can listen to several observables.

If I create every other observer, as shown below, then it will be simple, as shown below.

public class ConcreteObserver implements EventObserverA , EventObserverB {

    updateEventA(EventA event) {}
    updateEvetnB(EventB event) {}

}

In this case, I have to write a lot of different observable / observable classes / interfaces with almost the same piece of code inside.

To avoid issues like the one above, I would like to generate an observer /, but as you guys know that the multiple inheritance rule does not allow the use of code, as shown below.

public class ConcreteObserver implements Observer<EventA> , Observer<EventB> {

    update(EventA event) {}
    update(EventB event) {}

}

, , , , / .

, , , n: 1: , 1: n : .

?

Answer 1

Java 8 ConcreteObserver Observer<EventA> Observer<EventB>; - :

public class ConcreteObserver {
    observeEventA(EventA event) {}
    observeEventB(EventB event) {}
}

::updateEventA ::updateEventB ConcreteObserver , Observer<EventA> Observer<EventB>. , :

• Observer<EventA> eventAObserver = concreteObserver::updateEventA;
• Observer<EventB> eventAObserver = new ConcreteObserver()::updateEventB;
• observerRegistry.register(EventA.class, concreteObserver::updateEventA);