Open Hypermedia Systems Working Group

Beans, RMI, Voyager

What is a Java Bean?

Java Beans are Javasoft's approach to component oriented software development, that is making it possible to develop software components that relatively easily can be assembled into an application by an enduser or a programmer. The ability to be manipulated by a application builder tool (ABT) is the defining characteristic of a Java Bean.

A notable difference between Java Beans and other component architectures (such as COM or OpenDoc) is that Java Beans are Java-centric, exclusively targeted at software development in Java. To ease integration with the Windows platform, bridges between Beans and COM have been developed.

The architecture of a Bean

Java Beans do not extend a common superclass (apart from Object). Most of the behaviour of the Java Bean is defined by conventions and guidelines rather by implementing an interface or extending a 'bean' class. These conventions include

• Properties should retrieved and set with getProperty and setProperty methods respectively, rather than being accessed directly
• There should be a zero argument constructor
• There should be generated events to reflect changes in the Java Beans state
• The Java Bean should be persistent, i.e. implement java.io.Serializable

Following the above mentioned steps will allow an ABT to make basic customisation, but to provide more advanced possibilities, the Java Bean author can use

Introspection

By creating a 'BeanInfo' class alongside with the Java Bean itself, the author can provide precise information on the workings of the Java Bean

Bean editors

Most ABT provide editors for basic types, such as strings or integers. If the Java Bean has more complex properties, it can supply its own editors

Wizards

Some Java Beans are so complex, that they must be setup using wizards, also provided with the Java Bean.

Java Beans will often be visual, e.g. a GUI component, though this need not be the case, as long as it can be visually manipulated in an ABT.

Please send feedback to Niels Olof Bouvin. Last modified: Mon Dec 15 00:54:10 1997