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Capture hierarchical structures with Swing's JTree

Find out how Java's new standard tree component helps you to handle one of the most common programmatic functions

By Tomer Meshorer, JavaWorld.com, 10/01/98

Trees allow us to represent hierarchies of data in a convenient, accessible form. They are important because hierarchies of data are extremely common -- from the contents of your hard drive to the interconnections of a global public-key certification framework. Swing's JTree component enables developers to easily capture (represent in a data structure) and display hierarchies. Before Swing, there was no standard JDK tree component; furthermore, few of the third-party options were as well designed as this: Like all Swing components, JTree is built around the Model-UI pattern -- a design in which each component is divided into a model part that holds the data and UI part that renders it.

Rather than cram both aspects of the Model-UI pattern into one huge article, I've decided to split up the concept into two, more easily digestible articles. This month, I'll demonstrate how to use the model portion of JTree to capture hierarchical structures; look for my discussion of the UI portion sometime in early '99.

We'll begin with a brief look at the MVC architectural pattern and examine how it is integrated into Swing. Then, we'll move into a detailed discussion of the Swing tree package and its interfaces. Along the way, we'll examine listeners and various strategies for using the tree package. Finally, we'll bring our discussion to a close with a look at a simple program that demonstrates Swing's tree capabilities in action.

We've got a lot to cover, so let's get started!

A brief look at the MVC pattern

Swing's Model-UI architecture is a variation of the MVC (Model-View-Controller) pattern (see Resources). The MVC pattern, first introduced in Smalltalk-80, was designed to reduce the programming effort required to build systems that made use of multiple, synchronized presentations of the same data. The MVC consists of three distinct parts:

• The Model holds the data that is being represented.
  
  
• The View renders the data of the model. The view observes changes in the model and then renders the updated model data. Because there is only a single central model, all views will remain coherent.
  
  
• The Controller listens to user events and controls the view on the data.

The MVC pattern prompts the following software qualities, which make it such a novel idea:

MVC meets Swing

The MVC design pattern is typically used for constructing user interfaces that may present multiple views of the same data. The design pattern is extremely important because it completely de-couples data display from data representation. This means that the user interface of an application can be completely changed -- even dynamically, under direction of the user -- without need for any change to the underlying data subsystem of the application. As long as you can implement the model (TreeModel, more on this later), your view does not have to change.

 

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