This is one of the programming guidelines for beans. A Bean Builder application can recognize a property by looking for these methods, and it will make it possible for an application developer to manipulate these properties. To make it easier to work with properties, Java 1.1 defines a PropertyChangeEvent class and an associated PropertyChangeListener . A bean can generate a PropertyChangeEvent when one of its properties changes. A Bean Builder can check for this method to determine whether a bean supports property change events.
Swing uses the idea of properties and PropertyChangeEvents extensively.
It also adds a similar event type, ChangeEvent , which carries less information than a PropertyChangeEvent and can therefore be handled more efficiently. In addition to Swing, Java 1.2 introduces a few other new features. Java 1.2 also includes a greatly enhanced two-dimensional graphics capability. In addition to the graphics routines from the Graphics class, a Graphics2D object includes support for additional shapes, curves, lines that are more than one pixel thick, and dotted and dashed lines. In addition, it has support for geometric transformations, which means that it is possible to apply rotation, scaling, and translation operations to whatever is drawn in the graphics context.