Java Coding Problems

172. Implementing the Observer pattern

In a nutshell, the Observer pattern relies on an object (known as the subject) that automatically notifies its subscribers (known as observers) when certain events happen.

For example, the fire station headquarters can be the subject, and the local fire stations can be the observers. When a fire has started, the fire station headquarters notifies all local fire stations and sends them the address where the fire is taking place. Each observer analyzes the received address and, depending on different criteria, decides whether to extinguish the fire or not.

All the local fire stations are grouped via an interface called FireObserver. This method defines a single abstract method that is invoked by the fire ...