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Java Forum / General / March 2006force java version
is there a way to require a certain java version (or better) on the users machine? > is there a way to require a certain java version (or better) on the > users machine? You could politely ask the user to ensure that they have a certain version of Java on the download page, or shrink wrap packaging of your software, and offer to download and/or install the latest version for them. You could have your program detect the Java version and refuse to run for certain values. - Oliver > You could have your program detect the Java version and refuse to run for > certain values. That could cause ugly exceptions depending on (1) the JDK the app was built on and (2) the JRE the end user is running on. For example, I believe (this is from memory, so I could be wrong) if an app built on a Java 5 JDK is run on a JRE 1.4.x VM, an UnsupportedMajorMinorException is thrown due to the different serialVersionUID. >> You could have your program detect the Java version and refuse to run for >> certain values. [quoted text clipped - 5 lines] > UnsupportedMajorMinorException is thrown due to the different > serialVersionUID. So catch those, and show a pop up saying "Please upgrade your JVM". ;) - Oliver > So catch those, and show a pop up saying "Please upgrade your JVM". ;) :-) Then there's that. But actually, I think that would be thrown as soon as the main class is loaded, which I would think would stop any further execution of the program. >> You could have your program detect the Java version and refuse to run for >> certain values. [quoted text clipped - 5 lines] > UnsupportedMajorMinorException is thrown due to the different > serialVersionUID. You are indeed wrong. Alun Harford > For example, I believe (this is from memory, so I could be wrong) if an > app built on a Java 5 JDK is run on a JRE 1.4.x VM, an > UnsupportedMajorMinorException is thrown due to the different > serialVersionUID. Correction: I was mixing up class version with serialVersionUID. The actual exception that would be thrown is UnsupportedClassVersionError, with a message stating "Unsupported major.minor version 49.0". This would be thrown _as soon_ as the main class is loaded, before main() gets executed. So detecting older JREs programmatically would _not_ work... Hi, > For example, I believe (this is from memory, so I could be wrong) if an > app built on a Java 5 JDK is run on a JRE 1.4.x VM, an > UnsupportedMajorMinorException is thrown due to the different > serialVersionUID. You're thinking of UnsupportedClassVersionError (Unsupported major.minor version xx.x). Note however that you can "-target", say, an 1.4 JVM using an 1.5 compiler. Here's an example of the exception you're thinking of: ...$ java -jar /home/example/fakejar42.jar Exception in thread "main" java.lang.UnsupportedClassVersionError: com/fake/FakeJar (Unsupported major.minor version 49.0) The serialVersionUID isn't related to this however (which may be what Alun Harford was referring to but it's not clear from his very verbose and very informative post ;) >is there a way to require a certain java version (or better) on the >users machine? there is in Java Web Start. Further, an app can test the version early and refuse to run if it inappropriate. See http://mindprod.com/products1.html#COMMON11 for source code to do the test.  SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. are you talking about the download for "comparator"? its under - Common JDK 1.1+ Utility classes Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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