Teaching Software Componentization: A Bar Chart Java Bean

1. INTRODUCTION Modern-day software applications can be characterized as assemblages of portable software components. This has led to a new approach to software development, often called Component Based Development (CBD), which facilitates software reuse (Ratchivadranand and Rothenberger, 2003). The CBD approach is gradually working its way into programming curricula (Cunningham et al, 2 003; Howe et al, 2004). Most college-level computer programming classes in information systems curricula go into a fair amount of detail in building applications that use software components. A classic example would be in most Java courses, where students learn how to use many of the Swing GUI components (http://java.sun.com/javase/6/docs/api/javax/ swing/package-summary.html). Similarly, Microsoft's .NET API includes a broad collection of graphical components (called "controls" in the Microsoft world), for both Windows and Web applications, that are covered in programming courses using the .NET platform (http://msdn. microsoft.com/en-us/library/ms229335(v=VS.90).aspx). Learning how to use these components involves instantiation, placement in forms and containers, viewing and manipulating their properties, invoking behaviors via method calls, and responding to events generated by the components. These are the skill that most students get comprehensive training and practice in during their programming coursework. It is far less common to teach students how to actually build these components, which would involve designing and implementing the very properties, behaviors, and event-generation algorithms that would be necessary to deliver to applications using the components. In other words, seeing "the other side of the coin" is a gap in the knowledge of most students graduating from a CIS curriculum. This paper presents a sequence of two programming assignments that cover both sides of the coin, the component construction and the component usage. The first involves creation of a component that implements a bar chart, utilizing arrays of numbers and strings for the bar values and labels. In this assignment, students perform graphics programming, and implement listener registration and notification algorithms. The second assignment involves use of the bar chart component in an application that performs grouped aggregate queries on a database, generates the bar chart based on this aggregation and grouping, and responds to a user's click on a particular bar in order to obtain detailed information about the corresponding group. In the following sections, I will discuss the pedagogical benefits of the component-building-and-use approach, describe the bar chart component in general, and outline the programming tasks involved in creating and using the bar chart. 2. PEDAGOGICAL BENEFITS OF IMPLEMENTING AND USING JAVA-BASED GRAPHICAL SOFTWARE COMPONENTS In the Java world, graphical software components are implemented as JavaBeans (Liang 2009 pp1049-1064). For example, all of the Swing GUI classes in the Java Class Library are JavaBeans. JavaBeans are useful for rapid application development (RAD), because they provide developers with ready-made modular functional units that can typically be embedded in Java applications through an Integrated Development Environment's (IDE) form-building design tools. NetBeans, Eclipse, and JBuilder are examples of Java IDE's that include form-builders enabling JavaBean drag-and-drop design features. JavaBeans are specially configured Java classes that involve the following characteristics: (1) they must be implemented as public classes; (2) they must include default constructors (i.e. constructors that take no arguments; (3) they must be serializable (i.e. implement the Serializable interface); (4) they will typically include properties involving private member variables with associated accessor and mutator methods; and (5) they will typically generate events, and therefore include associated Listener interfaces and public registration and deregistration facilities (Liang 2009, p1050). …