CODEWITHSUNDEEP
javamacos
Keaton
Keaton

Reputation: 127

Run Java packages on unsupported Java Version

I have a PowerMac and it is giving me bad version number on some .jars. I would love to make it seem like I am running Java 6. How would I spoof the version? Let me also say I am running PowerPC and Leopard

Upvotes: 0

Views: 469

Answers (1)

Stephen C
Stephen C

Reputation: 719310

The most likely problem is that you have Java 6 JAR files and you are trying to run them on an old Java installation.

How would I spoof the version?

The answer to your question is that you can't. The way to run Java 6 specific JAR files it to use a Java 6 (or later) JRE or JDK.

The problem is that the format of Java class files has changed, and your installation can't cope with the new format. And this is not a gratuitous change that you can pretend doesn't exist. Java 6 (actually Java 5) has support for generic types, enums, annotations and other things. Assuming that the JARs contain code that uses these new language features, an older JRE simply won't know what to do with them.

There are two solutions:

  • Upgrade your Java installations to the required level on all machines. This is the best solution ... if it is an option ... because it means your users will get the benefit of security and bug fixes and performance enhancements. (And progress of your project won't be held back by the constraint of supporting legacy platforms.)

  • Compile all of your code for compatibility with the oldest version of Java that you still have to use. Either compile on the corresponding old JDK, or on a more recent JDK using appropriate -source / -target / -Xbootclasspath options ... as described by the javac manual page.

The catch with the second solution is that if the source code for the JAR files in question uses recently added Java language features or APIs, then recompiling for the older platform will fail. To fix this you will need to rewrite your code to replace the nice modern stuff with archaic stuff. Not a good solution, IMO.

The other possibility is that you are seeing corrupted JAR files. This is unlikely, but it can happen if you are using applets or webstart, and the server is delivering error pages instead of JAR files.

The third possibility is that you simply haven't configured your Mac's Java installation's correctly. Making Java 7 the default should allow you to run everything without class version problems. (Thanks @paulsm4) Note that I can't help you with that ... 'cos I don't use Java on a Mac.

Upvotes: 3

Related Questions