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Soup up your Java classes with customization

Wow your beans users with cool customization features

By Mark Johnson, JavaWorld.com, 12/09/97

Those of you who have been following this column have already read my first two installments on Java customization. The first,"Double Shot, Half Decaf, Skinny Latte: Customize your Java," was an introduction to the concept of object properties and the various ways in which beans can be customized. Last month's column, "The trick to controlling bean customization," covered the general concepts of bean customization structure, and was a bit light on code and examples. This month, we'll hit some more complex coding examples. The background to JavaBeans customization has been covered in previous articles, so this article will assume that you've either read those articles, or you have an equivalent understanding of the topic.

Because the more advanced JavaBean customization features are only necessary for more advanced beans, we'll start with a walk-through of ScatterPlot, a bean that displays a scatter plot of data it retrieves from another object. The ScatterPlot class will (perhaps predictably) provide us with some gnarly customization problems. Fortunately, we'll have the tools at hand to solve them, armed as we are with the customization interface of the JavaBeans API. We'll overcome some of the limitations of property sheets by writing and registering a property editor for a derived type, and we'll finish by writing a complete customizer class.

Property editors vs. customizers

To recap from last month's column, there's a difference between a property editor and a customizer. A property editor is a class that implements the java.beans.PropertyEditor interface (although it often does so indirectly, by extending the "adapter" class java.beans.PropertyEditorSupport). Its purpose is to allow the user to edit a single property of a bean. The BeanBox container, from Sun, comes with several built-in property editors that it presents to application developers in a property sheet, as follows. (For more on the BeanBox, see my previous JavaWorld article, "The BeanBox: Sun's JavaBeans test container." Check-out the Resources section of this article to download the BeanBox.)

Class	Property Editor
Boolean	BoolEditor
Byte	ByteEditor
Color	ColorEditor
Double	DoubleEditor
Float	FloatEditor
Font	FontEditor
Int	IntEditor
Long	LongEditor
Number	NumberEditor
Short	ShortEditor
String	StringEditor

Built-in BeanBox property editors

When the user selects a bean in the BeanBox, the BeanBox application builds a custom property sheet for the bean. It first introspects the bean to figure out what its properties are. Then, based on the class, the BeanBox places an instance of each of these property editors, one per property, along with labels identifying the properties. Any properties for which it either can't find or (for some reason) can't construct property editors are omitted from the property sheet. This means that any properties for which no editor exists, including properties of types you've created, won't show up on the property sheet, even if appropriate setter and getter methods have been written for them. (This is an important point, as we'll see later.)

 

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