Learning Java

Building Beans

Now that you have the feel from the user’s perspective, let’s build some Beans. In this section we will become the Magic Beans company. We will create some Beans, package them for distribution, and use them in the BeanBox to build a very simple application. (The complete JAR file, along with all of the example code for this chapter, is on the CD-ROM that accompanies this book, and at http://www.oreilly.com/catalog/learnjava.)

The first thing we’ll remind you of is that absolutely anything can be a Bean. Even the following class is a Bean, albeit an invisible one:

public class Trivial implements java.io.Serializable {}

Of course, this Bean isn’t very useful: it doesn’t have any properties, and it doesn’t do anything. But it’s a Bean, nonetheless and you can drag it into the BeanBox. It’s important to realize that JavaBeans really doesn’t give a hard and fast definition for what a Bean is required to be. In practice though, we’ll want Beans that are a little more useful.

Creating a Component with Bindable Properties

We created a nifty Dial component in Chapter 15. What would it take to turn it into a Bean? Well, surprise: it is already a Bean! The Dial has a number of properties that it exposes in the way prescribed by JavaBeans. A "get” method retrieves the value of a property; for example, getValue( ) retrieves the dial’s current value. Likewise, a “set” method (setValue( )) modifies the dial’s value. The dial has two other properties, which also have “get” and “set” ...