具有多个可观察的单个观察者

Question

I would like to know what would be the implementation with respect to observer design pattern. Like generally we maintain a list of observers in Observable and from its notify we call the update method of the observers.

Now what would be the design in this case? Should i maintain a list of observable in the observers? But then in the update method how i would know which observable has called the update on this observer.

Please share your idea on this.

Thanks,

Answer 1

Usually the observable hold a reference to the observer. in your case this mightg be a list. in any case, the first argument to update is the observable.

So this is one way:

import java.util.Observable;
import java.util.Observer;
enum Observables {
    o1,o2
}
class MyObservable extends Observable {
    public MyObservable(Observables observables) {
        this.observables=observables;
    }
    public void setChangedAndNotify(Object object) {
        setChanged();
        notifyObservers(object);
    }
    final Observables observables;
}
class MyObserver implements Observer {
    @Override public void update(Observable o,Object arg) {
        switch(((MyObservable)o).observables) {
            case o1:
                System.out.println(((MyObservable)o).observables);
                break;
            case o2:
                System.out.println(((MyObservable)o).observables);
                break;
        }
    }
}
class so56200126_single_observer_with_multiple_observable {
    public static void main(String[] args) throws InterruptedException {
        MyObservable myObservable1=new MyObservable(Observables.o1);
        MyObservable myObservable2=new MyObservable(Observables.o2);
        MyObserver myObserver=new MyObserver();
        myObservable1.addObserver(myObserver);
        myObservable2.addObserver(myObserver);
        myObservable1.setChangedAndNotify(null);
        myObservable2.setChangedAndNotify(null);
        Thread.sleep(1);
    }
}