Listeners as Extension Points

The phrase extension point is used in software development to indicate a place in a framework or application where the creators expect users to extend or customize the framework to meet their needs. (You will also hear the word hook used for the same meaning.)

Quartz listeners are a type of extension point in which you, as a Quartz user, can extend the framework and customize it to do new things. This customization takes place within the listener class implementations that we show you how to build in this chapter.

Listeners are not the only extension points in the framework. Along with plug-ins and a few other customization options, listeners provide a simple means of customizing the framework and making it do what you need it to do. Because the extension points for listeners are supported through a publicized interface, you don't have to worry about creating your own branch of the code that then is unsupportable.