Chapter 2. The Observer Pattern: Keeping your Objects in the know

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Don’t miss out when something interesting happens! We’ve got a pattern that keeps your objects in the know when something they might care about happens. Objects can even decide at runtime whether they want to be kept informed. The Observer Pattern is one of the most heavily used patterns in the JDK, and it’s incredibly useful. Before we’re done, we’ll also look at one-to-many relationships and loose coupling (yeah, that’s right, we said coupling). With Observer, you’ll be the life of the Patterns Party.


Your team has just won the contract to build Weather-O-Rama, Inc.’s next-generation, Internet-based Weather Monitoring Station.

Statement of Work

Congratulations on being selected to build our next-generation, Internet-based Weather Monitoring Station!

The weather station will be based on our patent pending WeatherData object, which tracks current weather conditions (temperature, humidity, and barometric pressure). We’d like you to create an application that initially provides three display elements: current conditions, weather statistics, and a simple forecast, all updated in real time as the WeatherData object acquires the most recent measurements.

Further, this is an expandable weather station. Weather-ORama ...

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