javautilObservable

The java.util.Observable class was a fundamental part of Java's observer pattern implementation before its deprecation. It provided a mechanism for objects to notify other objects when their state changed. An Observable object maintained a list of observers and would notify them by calling their update() method. The update() method typically received a reference to the Observable object that triggered the notification.

To use Observable, a class would extend it. Then, other classes, designated as observers, would implement the java.util.Observer interface. An observer would register itself with an Observable instance by calling the addObserver() method. When the Observable's state changed, it would call its setChanged() method, which flags the object as having changed. Subsequently, calling the notifyObservers() method would iterate through the registered observers and call their update() method.

While Observable was widely used, it had certain limitations. It was not thread-safe, requiring developers to implement their own synchronization mechanisms. Furthermore, the Observer interface only allowed passing the Observable object itself to the update method, making it challenging to pass specific data about the change. Due to these and other design considerations, the java.util.Observable and java.util.Observer classes were deprecated in Java 9. Modern Java development typically favors alternative approaches like event listeners, property change support, or dedicated reactive programming libraries.