java.lang.UnsupportedClassVersionError

Question

When I ran a java program I received this error.. Could you please suggest why do we get this error:

Exception in thread "main" java.lang.UnsupportedClassVersionError: 
    GenerateInvoice (Unsupported major.minor version 49.0)
        at java.lang.ClassLoader.defineClass0(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:539)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:123)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:251)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:55)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:194)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:187)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:289)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:274)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:235)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:302)

Answer 1

This class was compiled with a JDK more recent than the one used for execution.

The easiest is to install a more recent JRE on the computer where you execute the program. If you think you installed a recent one, check the JAVA_HOME and PATH environment variables.

Version 49 is java 1.5. That means the class was compiled with (or for) a JDK which is yet old. You probably tried to execute the class with JDK 1.4. You really should use one more recent (1.6 or 1.7, see java version history).