Java Examples in a Nutshell, 3rd Edition

Specifying Bean Information

The YesNoPanel class itself, as well as the MultiLineLabel, Alignment, AnswerEvent, and AnswerListener classes it relies on, are all a required part of our bean. When an application that uses the bean is shipped, it has to include all five class files. There are other kinds of classes, however, that are often bundled with a bean but not intended for use by the application developer. These classes are used at “design time” by the beanbox tool that manipulates the bean. The bean class itself doesn’t refer to any of these auxiliary beanbox classes, so it is not dependent on them, and they don’t have to be shipped with the bean in finished products.

The first of these optional, auxiliary classes is a BeanInfo class. As explained earlier, a beanbox discovers the properties, events, and methods exported by a bean through introspection based on the Java Reflection API. A bean developer who wants to provide additional information about a bean, or refine the (somewhat rough) information available through introspection, should define a class that implements the BeanInfo interface to provide that information. The ShowBean class, for example, uses the short descriptions it obtained through a BeanInfo as tooltips in its Properties menu.

A BeanInfo class typically subclasses SimpleBeanInfo, which provides a no-op implementation of the BeanInfo interface. When you want to override only one or two methods, it is easier to subclass SimpleBeanInfo than to implement BeanInfo ...