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Become a programming Picasso with JHotDraw

Use the highly customizable GUI framework to simplify draw application development

By Wolfram Kaiser, JavaWorld.com, 02/16/01

Software developers want to build software applications quickly and still focus on quality. One way to reduce development time and improve software quality is to use a framework. Frameworks are designed for reuse; they offer prefabricated components as building blocks and design patterns as blueprints for the architecture.

Many Java programmers frequently use a framework -- maybe even without realizing it. JFC Swing can be viewed as a rather simple framework for creating almost all general-purpose graphical user interfaces (GUIs). Although you can use it for many applications, JFC Swing lacks a clear structure for a GUI-based application. A more specific framework in that respect is JHotDraw (see Resources for a link), which targets applications for drawing technical and structured graphics -- such as network layouts and Pert diagrams -- and offers much better support to develop editors for those purposes. JHotDraw demonstrates frameworks' power and usefulness within their application domain. Before I examine JHotDraw in detail, I'll discuss frameworks and the concepts they embody.

Theory of frameworks and design patterns

By using frameworks, developers usually reuse not only code, but also the design and architecture of a prototype application. Consequently, frameworks must be tailored to meet the needs of the problem domain. Unlike a class library, frameworks provide not only components, but also a structure for integrating those components, a predefined interoperation of components, and often a basic skeleton of an application. The skeleton is not passive like a class library, but has its own execution path from which user-defined component code is called, resulting in an inversion of control.

Developers often face problems in software design that are recurring and typical of a certain situation. You can capture a proven solution to those problems in a design pattern. A design pattern describes a problem, its context, and a reusable solution. It also assigns the problem a meaningful name, which can be used to communicate the solution to other developers.

Frameworks often rely on design patterns to help achieve a flexible general-purpose application design. The patterns introduce indirections and abstractions, which let you plug in your own classes and components.

A framework helps create an application that is developed in a timely manner and customized to the user's requirements, and still benefits from the framework's maturity with regard to robustness and stability. However, this result comes at a price -- the cost of learning and understanding a framework's interactions and even limitations. Most frameworks are rather complex pieces of software at high levels of abstraction. Understanding a framework can be difficult, and debugging framework code is sometimes cumbersome. Frameworks offer some customization facilities, but they can impose some restrictions and may require special programming techniques, especially if you want to perform functionality slightly out of the framework's defined scope.

 

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