Testing against OCP
What if we need to add another type of reporting say
PDFReporter? Obviously, as ReporterServlet needs to be altered
in order to accommodate this third type of reporting capability.
Worse is the case, if we don’t want one of the existing type of
report any more. Even then, we need to go back to the
ReporterServlet and accommodate the change. Clearly, this is
against OCP. This design is not closed for modification and is
not open for extension.
OCP compliance
Clearly, the solution is to make the ReporterServlet depend on
an abstraction of the ReportWriter. This way, the underlying
implementation will not affect the ReporterServlet code to
change. The design in Figure 4 is OCP compliant solution:
The classes in a package are reused together. If you use one of
the classes in a package, you reuse all the classes in that
package.
Figure 4: The OCP compliant design for the ReportWriter
component
Test against DIP
The design in Figure 4 is OCP compliant and also maintains
the principle of Dependency Inversion. Previously, the high-level module the
ReporterServlet had a strong coupling with the concrete implementation of the individual
Reporter. Now both the high-level module and the low-level XXXReporter
implementations depend on the abstraction viz. Reporter interface.
New on the Java Boutique:
New Review:
Time Management Made Easy with the Quartz Enterprise Job Scheduler
Why not just use the Java timer API? This open source scheduling
API boasts simplicity, ease-of-integration, a well-rounded feature
set, and it's free!
New Applet:
Reverse Complement
Reverse Complement is a simple applet that converts DNA or RNA
sequences into three useful formats.
Elsewhere on internet.com:
WebDeveloper Java
Lots of Java information on webdeveloper.com
WDVL Java
Thorough Java resource at the Web Developer's Virtual Library.
ScriptSearch Java
Hundreds of free Java code files to download.
jGuru: Your View of the Java Universe
Customizable portal with online training, FAQs, regular news updates, and tutorials.
