Java Glossary : JavaBeans

Java definitions: 0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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A standard for Java componentware. It functions much like Microsoft's Windows-specific VBX Visual Basic pluggable components. The JavaBeans APIs allow ISVs to develop reusable software components that end-users can then hook together using visual application builder tools, such as Inprise's JBuilder, IBM's Visual Age, SunSoft's Java Workshop and Symantec's Visual Café. For example, Visual Café Pro has already created many smart components to give Delphi-like abilities to crank out SQL database applications. JavaBeans have persistence (with serialised customised objects stored in *.ser pickle files), properties, events and methods that are exposed to the GUI designer. They also support "introspection" so that GUI builder tools can examine them to figure out what properties and methods they support.
Writing a Bean is easy.

They require a public parameterless default constructor.
Beans must be totally freestanding. They can't presume anything has been done for them ahead of time. If they need it, they have to create it or fake it for themselves. For example, they can't presume some static call has been done to set up a Window for them to display error messages. Beans are like little reptiles that must be able to fend for themselves the moment they hatch (are constructed).
A bean has no special interface to implement, just the dummy Serializable. There is a formal JavaBean Specification though.
Just use the standard getXXX, setXXX naming conventions for your properties and make public the ones you want to expose. You can hide some of the public properties later in your BeanInfo to give you the Delphi-like distinction between public and published.
String properties should be initialised to "" or some value rather than null.
Provide a BeanInfo class to describe the properties. BeanInfo classes can get pretty elaborate, but writing a minimal one is very simple. I have provided some sample source under BeanInfo. It theory, you can have a bean without a BeanInfo, but it best to write one, even if just to provide an icon.

Usually beans are bundled up with their corresponding BeanInfo classes into jar files.
Many companies are selling JavaBeans you can plug into your own custom applications. I have some I have written available free with source code. They handle prompting, data validation and generating error messages for data keyed. There are plain and dbaware components for dates, FormattedTextFields, phone numbers, provinces, postal codes, etc. you can download.

Mastering JavaBeans

0-7821-2097-0

Laurence Vanhelsuwé

800-pages. Now out of print. Available free in PDF form.

Companies selling beans include ProtoView Jsuite, Rogue Wave, SoftTech, StingRay, KL Group JClass and Three D Graphics.

BeanBox ¤ BeanInfo ¤ Gembuilder ¤ introspection ¤ jar file ¤ Java Studio ¤ manifest ¤ pickle file ¤ Stingray ¤ Sun's JavaBean Spec

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