More Details on Writing JavaBeans
The beans shown in the previous section were all examples of beans with a visual interface. All Java components, such as applets and buttons, are beans and any subclass may be a bean with a visual interface.
Other Java classes may also be beans. Without a visual interface, they don’t show in a builder tool such as the Beanbox, but they may have methods that are useful to be linked from other beans.
The builder tool uses introspection to analyze the names of the methods of a class to determine its properties, methods, and events in order to be used as a bean.