UnsupportedClassVersionError while running Java program

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Exception in thread “main” java.lang.UnsupportedClassVersionError: a (Unsupported major.minor version 51.0)

My Java program which I run on Mac & Windows is not working. Instead I get this error:

Exception in thread "main" java.lang.UnsupportedClassVersionError: menus/Main_Screen : Unsupported major.minor version 51.0
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
    at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)

Does anyone know how to fix this? Thanks.

Have you tried using the `-source` and `-target` flags to specify the bytecode version you want? E.g. `-target 6`. — Mike Samuel, Jan 17 '13 at 18:52

score 3 · Answer 1 · answered Jan 17 '13 at 19:11

3

Class version 51.0 is generated by Java 7.

You're trying to run with an earlier version, probably Java 6. You need to call the Java 7 version of the java command.

The version used to run NetBeans is set in NetBeans/etc/netbeans.conf.
The version used to build and run a project is set by the project properties.
You can tell NetBeans about a new Java version through the Tools > Java Platforms

answered Jan 17 '13 at 19:11

Devon_C_Miller

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sorry, but how to do it? cos im not very familiar with it – Ameera Rio Jan 17 '13 at 19:22
Install the latest JDK (1.7u11, at the moment) from here: http://www.oracle.com/technetwork/java/javase/downloads/index.html – Devon_C_Miller Jan 18 '13 at 15:19
Alternatively, in NB, right click your project, choose properties, and change target/binary to JDK-6 – Devon_C_Miller Jan 18 '13 at 15:37

score 0 · Answer 2 · answered Jan 17 '13 at 18:50

0

Unsupported major.minor version 51.0 at java.lang.ClassLoader.defineClass1(

It seems your java runtime version is different (lower) version from compile time version.

answered Jan 17 '13 at 18:50

kosa

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what is the solution? how to change it? i have 3 main classes – Ameera Rio Jan 17 '13 at 19:17
Make sure Java version on Mac is same as Java version on your windows. – kosa Jan 17 '13 at 19:35

score 0 · Answer 3 · answered Jan 18 '13 at 03:35

The general rule is this.

If take a *.class compiled by a version of Java EARLIER than the JRE, it should work in that JRE. Because the later JRE is supposed to "know" previous versions of format.

If take a *.class compiled by a version of Java LATER than the JRE, it should not work in that JRE. Because the earlier JRE is not supposed to know the future versions of format.

In your case the code is simply compiled by the version of Java issued after the version of the JRE.

UnsupportedClassVersionError while running Java program

3 Answers3