Exam: Completing the Observer Pattern in WeatherStation

Description

In this exam, we will complete a Weather station service, which constantly send weather data its subscribers. The service is implemented via the Observer design pattern. The architecture is shown below:

The key elements in the design are:

• WeatherStation.java: The main test file.
• WeatherData: Save the weather revelent data including temperature, humidity, and pressure.
• Subject.java: Add / remove observers to an internal array
• Observer.java: Observer interface.
• DisplayElement.java: Display interface.

The other two files StatisticsDisplay.java and CurrentConditionDisplay.java implement the observer and display interface. The code was adapted from Head First Design Pattern.

Objective

In this exam there are two main tasks.

1. You need to complete the 3 functions in Subject.java:

   public void registerObserver(Observer o) { }
   public void removeObserver(Observer o) { }	
   public void notifyObservers() { }

   By default, each function will print

   Please remove this line and implement ...
   

   Remove the message and enter your code.

2. You need to complete the update() functions in StatisticsDisplay.java and CurrentConditionDisplay.java.

Expected Output

The output example of the CurrentConditionsDisplay is:

Current conditions: 80.0F degrees and 65.0% humidity

The StatisticsDisplay shows the average, max and min temperatue. The output example is shown below:

Avg/Max/Min temperature = 81.0/82.0/80.0

The good news is that the output functions have already been implemented. You don't need to modify them. Enjoy the exam!