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Observer pattern usage example

Pragya Keshap answered on February 15, 2023 Popularity 6/10 Helpfulness 1/10

answer Observer pattern usage example

Observer pattern usage example

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@Test
public void observersHandleEventsFromSubject() {
   // given
   Subject<String> subject = new ConcreteSubject();
   Observer<String> observerA = Mockito.spy(new ConcreteObserverA());
   Observer<String> observerB = Mockito.spy(new ConcreteObserverB());

   // when
   subject.notifyObservers("No listeners");

   subject.registerObserver(observerA);
   subject.notifyObservers("Message for A");

   subject.registerObserver(observerB);
   subject.notifyObservers("Message for A & B");

   subject.unregisterObserver(observerA);
   subject.notifyObservers("Message for B");

   subject.unregisterObserver(observerB);
   subject.notifyObservers("No listeners");

   // then
   Mockito.verify(observerA, times(1)).observe("Message for A");
   Mockito.verify(observerA, times(1)).observe("Message for A & B");
   Mockito.verifyNoMoreInteractions(observerA);

   Mockito.verify(observerB, times(1)).observe("Message for A & B");
   Mockito.verify(observerB, times(1)).observe("Message for B");
   Mockito.verifyNoMoreInteractions(observerB);
}

Popularity 6/10 Helpfulness 1/10 Language java

Source: Grepper

Tags: java observer-pattern

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Contributed on Feb 15 2023

Pragya Keshap

0 Answers Avg Quality 2/10

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