observer

Observer Design Pattern

Observer Design Patter specifies communication between two side objects: observable and observers.

An observable is an object which notifies observers about the changes in its state.

Example

A news agency can notify channels when it receives news.

Receiving news is what changes the state of the news agency, and it causes the channels to be notified.

Remarks

• NewsAgency is observable.
• Channel is observer.

Test

NewsAgency observable = new NewsAgency();
NewsChannel observer = new NewsChannel();

observable.addObserver(observer);

// it will notifiy observer by calling ovserver method
// and observer set news
observable.setNews("A breaking news"); 

Assertions.assertEquals(observer.getNews(), "A breaking news");