Java AWT Reference

4

Events

In this chapter:

• Java 1.0 Event Model
• The Event Class
• The Java 1.1 Event Model

This chapter covers Java's event-driven programming model. Unlike procedural programs, windows-based programs require an event-driven model in which the underlying environment tells your program when something happens. For example, when the user clicks on the mouse, the environment generates an event that it sends to the program. The program must then figure out what the mouse click means and act accordingly.

This chapter covers two different event models, or ways of handling events. In Java 1.0.2 and earlier, events were passed to all components that could possibly have an interest in them. Events themselves were encapsulated in a single Event class. Java 1.1 implements a “delegation” model, in which events are distributed only to objects that have been registered to receive the event. While this is somewhat more complex, it is much more efficient and also more flexible, because it allows any object to receive the events generated by a component. In turn, this means that you can separate the user interface itself from the event-handling code.

In the Java 1.1 event model, all event functionality is contained in a new package, java.awt.event. Within this package, subclasses of the abstract class AWTEvent represent different kinds of events. The package also includes a number of EventListener interfaces that are implemented by classes that want to receive different kinds of events; they define ...