Hello
I have received my
SCJD certification results and got 400 out of 400 points! I guess in this case I don't have to give you the split-up for the individual topics (GUI, Networking, ...)
At first I believed that it was a mistake, but after an e-Mail confirmation from Prometric it seems I really achieved the high-score ;o) As some of you might be interested in my design choices, I will give a brief overview over my assignment here.
But first things first: I would like to thank all people for the interesting and helpful discussions on javaranch.com, that helped me a lot for my assignment! The most helpful information came from Ken Krebs and his
thread about his very good score (
https://coderanch.com/t/184523/java-developer-SCJD/certification/NX-Notes-design-passed&p=). I have followed many of his advices during my assignment.
Summary - Assignment: URLyBird 1.3.3
- Implementation:
Java 5.0
- Networking: RMI (I didn't even bother to look into Sockets as RMI is so simple...)
- 22 Java source files (means 22 + a few (anonymous) inner classes)
- 107 kBytes of Java source code in total, including comments
- 4 kBytes for userguide.txt
- 5 kBytes for choices.txt
- 5 sub-packages inside "suncertify" package
-
IDE: Eclipse 3.1
Architecture As Ken, I chose a 3-tier design:
- GUI layer
- Service layer
- Backend layer with DB and locking
This makes it easy to switch between standalone and networked mode by simply changing the service layer from a local to a remote (RMI) version.
I have used logging extensively, mostly method entry/exit plus at some relevant branching points. Logging just went to the console. I applied test-driven development which I really love and thus used
JUnit for automated
testing. This was a real time saver and gave me confidence about the application, because the total development time was about one year because I was quite busy in my job. Being able to quickly re-run all tests after a few weeks of pausing and seeing the green bar in Eclipse really gives a good feeling

)
The build process was based on an
Ant script that performed compilation, unit testing, Javadoc generation and final JAR packaging. Also a big time saver.
Application Startup A main application class handles the startup parameters. It first builds the service layer, which means that it either constructs a local service layer for standalone mode or tries to get the published RMI version from the RMI registry for networking mode). Then, the GUI is built using the service layer. Note that the service layer is responsible for starting the backend layer because it's its only user.
If something goes wrong during GUI construction, a simple error message (no stack trace!) is printed on the console and the application terminates. Stack traces and the like are, however, logged. As soon as the GUI is visible, further problems also result in user-friendly error messages, but are displayed in dialogs.
GUI Layer My GUI is really simple. There's one "Edit" menu with an "Exit" item only. The table is quite basic too, with no sorting, no icons, no smart column width stuff. The "Smoking" column is, however, displayed as nice checkboxes.
I did not use icons anywhere, just plain text labels whose texts are simply hardcoded in the source file. Everything is held together by a few BorderLayouts and GridBagLayouts. Most GUI widgets have an informative tooltip text attached. Still, I provided an external userguide.txt file.
Note that contrarily to the classic model-view-controller (MVC) approach, I did not use a dedicated data model or a dedicated controller class. There is, however, a TableModel behind the JTable that holds list of HotelRooms. The HotelRoom class is a nice OO abstraction of a record in the database. Controller functionality is implemented as a set of anonymous inner ActionListeners that are attached to the relevant GUI elements (JButtons, JCheckBoxes etc.). They call methods in the service layer and may update the table model (if a search was triggered).
Note that I did not use the observer
pattern, as there is no such thing as a data model that could fire events. Data is basically sucked out of the service layer and pushed into the table model by the ActionListeners.
Also note that there is only a GUI for the client-side of the application. The network server runs without a GUI, except for configuration. After the server configuration is done, the configuration window closes and the server runs in the console window. This is sufficient as the only possible operation on the network server is stopping it. This can be done by pressing CTRL-C, thus just terminating the JVM.
I have underestimated the configuration GUIs. It was quite a bit of work to handle the three different application modes and the corresponding configuration GUI elements and their validation.
Service Layer I followed Ken's advices pretty closely here, so please consult the "Networking" and "General" paragraph the link I gave above.
Locking Same here, have a look at "Locking" in Ken's description. I did, however, use classic synchronization (using the synchronized keyword) instead of using Lock objects as Ken did.
Database Again, I pretty much followed Ken here, so have a look at his "Persistence" section.
General - I used Eclipse's auto-formatter for formatting. Sometimes this doesn't look nice and manual correction would have been an improvement, but I was too lazy

) But apparently you can get the full score by using auto-formatters.
- 48 hour booking hour rule was ignored and justified in choices.txt.
- The DBMain interface specifies for the create method that a new record is created in the database, "possibly reusing a deleted entry". For simplicity, I decided not to reuse deleted entries, but instead always append records to the end of the database file. This makes things much simpler. Make sure you also put such decisions in the choices.txt file.
- The database schema (field lengths etc.) are hardcoded in my source code because the schema is not going to change. That's at least how I justified it
- The update and delete methods specified by DBMain were correctly implemented in the Data class. However, no GUI controls for this functionality are provided, except for booking which eventually calls update.
I hope that this information is of any use for some of you. Please feel free to ask further questions.
Regards
Kaspar