Upgrade from JDK 1.2.2 to JDK 1.4.2. Any code changes required?

Question

Hi,
We are in the processes of upgrading the JDK versions on servers to JDK 1.4.2 to support other software upgrades.
The JDK versions on each of the servers are at different versions. On one of the servers, the version of JDK is currently at JDK 1.2.2_10. Can somebody please advise me if there would be any code changes required to support this upgrade (such as some methods being depreciated)?
We are also evaluating if we need to upgrade to JDK 1.4.5. In such a case, would there be any code changes required to upgrade from JDK 1.4.1_x to JDK 1.4.5. I assume there wouldn't be any changes for this minor upgrade but just want to confirm.
I would really appreciate an early reply.
Thanks in advance.
Regards,
Vamshi

Answer 1

"1.4.5" - you meant "1.5" ? :)
About deprecations -- you will be warned by the compiler. E.g. "assert", "enum" are keywords and cannot be used as method names.
The rest depends on your application. The more complex it is, the more differences can be encountered. You certainly need to run a test cycle for it with the new platform.
From my experience, I can list some issues that I have read about or have experienced myself:
1) serialization: the algorithm used to calculate the serialVersionUID had some changes between Java versions, due to compiler-added extra methods.
If you don't have serialized instances, or your serialVersionUID is specified explicitly, you are safe.
2) class loading order can be different in different platforms
Once ago I have seen a paper from BEA Systems highlighting some open topics that can arise when migrating between different vendor's JVMs. Probably, it is the one:
http://edocs.bea.com/jrockit/geninfo/devapps/codeprac.html
In my friend's case, there was some class-initialization logic, that behaved differently when class loading order changed.
3) Swing applications can sometimes behave slightly different.
E.g., I observed some changes in focus handling, although minor ones. Fixed with several lines of code.
4) Some libraries can depend on particular J2SE version. E.g. J2EE ones.
E.g. I was not able to run J2EE 1.4 thick client application with JRE 1.5. The j2ee library used by the app either had some dependencies on sun.* classes, or on some protocols (not sure, I don't remember it well).
5) Regression bugs are sometimes encountered. I.e. something that worked, does not work now.
Summary: You need testing.