Objectives and Deliverables
This chapter is from the book
This chapter is from the book
This chapter is from the book
Terms you'll need to understand:
Assignment requirements
Graphical user interface (GUI)
Javadoc
Techniques you'll need to master:
Making software design decisions by analyzing requirements
Providing a complete application as one JAR file, following the detailed instructions provided
In this chapter, you review the objectives and deliverables for the Sun Certified Java Developer (SCJD) certification. Because this certification has an assignment (the Sun Certified Enterprise Java Architect exam also has an assignment), it differs from most certification exams. In fact, the moderately difficult assignment, which can take months to complete, separates it from most industry certifications, which are usually proctored exams.
Objectives
The following are the main objectives for this certification:
Write an application program with Java. The application requires the following:
A graphical user interface (GUI) demonstrating good Human/Computer Interaction (HCI) principles of design.
A network connection, using RMI or sockets, to connect to an information server.
A network server that connects to the database; its skeleton is included in the download.
A database created by extending the functionality of the skeleton code, which comes with limited documentation.
In the DESIGN_CHOICES.TXT document and essay exam, you are asked to list some of the major choices you made for your design and implementation.
In the DESIGN_CHOICES.TXT document and essay exam, you are asked to list some of the main advantages and disadvantages of each of your choices.
In the DESIGN_CHOICES.TXT document and essay exam, you are asked to justify your choices by comparing your design and implementation objectives, including the advantages and disadvantages of each.
TIP
The database does not use Java Database Connectivity (JDBC). Rather, it is a simple file reader/writer supplied by Sun. Also, Sun supplies the data file, called database.bin. Sun wants you to create a database from these two elements.
The challenge is to convince the Sun evaluator that you understand how to build a client/server application that meets a given set of requirements. Along the way, this certification helps you understand and model a business need. I hope, however, that this book provides a solid guide to identifying and refining Sun's instructions and requirements. Although these requirements are written with or without formal language for requirements, they are good enough to see what you can do.
A better way to certify developers is to define a project by using standard documentation. For example, the SCJD certification's quality and utility would be improved if Sun used a three-part process. First, Sun would provide a project charter with a few owner interviews, the software objectives, and the overall purpose. Using this information, you would write a formal Software Requirements Specification (SRS; IEEE standard 830-1993, "Recommended Practice for Software Requirements Specifications") for that project. You would then exchange your SRS for Sun's by uploading your SRS and downloading Sun's SRS. Second, you would write a design document meeting those requirements, following the IEEE standard 1016.1-1993, "Guide to Software Design Descriptions." Third, you would exchange your design document for Sun's (which is what your design document is graded against) and write code to that document. This process is better and closer to reality. More important, it removes the ambiguity every candidate finds in the current instructions bundled in the assignment package.
Some would argue that my suggested certification process would be too difficult to standardize. Perhaps the reverse is true: Because the current assignment instructions are in nonstandard form, using industry-standard documentation and the software development life cycle would improve consistency and quality, representing a more reliable measure of a developer's skill.
GUI Design
One of the key ingredients for earning top marks is to design a clean interface for the user. As the human interface designer, you need to choose the interface components and lay them out proportionately. Java makes the nuts-and-bolts aspect of this exercise straightforward. Chapters 13, "The GUI," 14, "The Swing Components and Event Handling," and 15, "The JTable Component," discuss this topic at length. For now, please be aware that although there are many ways to build the screens for your assignment, Sun will surely appreciate your project following its recommended design guidelines.
The Java look and feel provides a distinctive platform-independent appearance and standard behavior, which is why one of the requirements specifies that you use Swing components, not Abstract Windowing Toolkit (AWT) components. Using the single look and feel that Swing provides helps ensure that what you see is what the evaluator will see. Sun wants to know whether you can take advantage of built-in Swing components. For example, you must use the JTable component. It is a helpful grid component, and feeding data into it is easy. However, the event model takes a little getting used to.
Database
The heart of the project is the database. Sun provides the skeleton pieces, which you must use to build your database. It is not as big a task as it sounds. The base classes Sun provides are already good enough. You just have to decide how much to modify the main piece (Data.java) and what you need to add in any additional classes. One common mistake is to overengineer the solution. My database met all the requirements and seemed to be a clean design, yet I added only two classes and didn't modify any Sun-supplied code. I've read many forum posts from developers who were looking for help on their code, but had clearly gone too far. What they were doing was unnecessary, or worse, obscured the real functionality they should have built.
One major ingredient of the database design is the locking mechanism. Chapter 7, "Databases and Atomicity," discusses the details of a good lock manager, the better way to go for this project. One hidden requirement is that only the client who locks a row can unlock it. This means there has to be a way to track clients within the locking mechanism. I've seen some clever ways to tackle it and some truly bizarre approaches that would surely lose points. A tricky part is what to do if the client locks a record and then dies. One elegant way to handle that situation is to let the system worry about it rather than invent some polling or timed checker design. This method is also explained in Chapter 7.
Networking
The assignment demands two modes of operation. The client that presents the information must be able to get it from a local database file or a remote one. The local mode is simple to implement, but the remote mode is harder. You have to design the network piece with RMI or sockets. Most people use RMI because it came later than sockets and is built on top of them. The early version of RMI was crude, but the current version, although it still needs another revision, is a better choice for this assignment than naked sockets. The big problem with sockets is thread management; you have to manually handle threads. RMI takes care of threads automatically, so the code is simpler. Some want to argue the merits of one over the other, but why not do that after passing the certification exam? I don't think sockets are worth the effort for this project. However, you might love them, so I talk about them in Chapters 11, "Networking with NIO," and 12, "RMI." Unlike the database classes, Sun provides nothing to get you started on the networking portion of the assignment.
Database Transparency
You can write a lot of fancy code so that the client handles the local database interaction one way and the network database another way. Here's a hint, however: If you design your solution the best way, there is no local– or network mode–specific code in the client. That is one of the challenges: Can you design the architecture in such a way that the database location is transparent to the client? The solution to this challenge is elegant, but not obvious. The trick is to use one interface, but have the signatures present the exact same types to the client when the database methods are called, regardless of whether the database was created by the factory from a local file or on the other side of the network through RMI. Also, the assignment forces you to build a database connection factory that generates a local or remote database connection based on command-line parameters. This factory is a marvelous example of the power behind design patterns. This design pattern is demonstrated in Chapter 9, "Interfaces," where you see a clear reason for having interfaces.
Design Choices
Some people can code fast and furiously. However, they are taking chances and might overlook important details, so what they end up doing is quickly building something that will fail even faster. There are many ways to design the GUI and the network pieces, but you need to make sure you are using a reasonable approach and are able to justify why you chose it.
One of the documents you must include in your certification project is the DESIGN_CHOICES.TXT file. In it, you list some of the major design choices you made and explain your choices by describing their main advantages and disadvantages. Also, you need to compare the design and implementation objectives with the advantages and disadvantages of your choices.