NetBeans project JAR won't run after clean and build?

Question

Inside one of my Netbeans projects, as jar is built and run perfectly. However, when the same project is cleaned & built, the lib folder is absent from dist and the generated jar does not run and produces the following CMD prompt message:

    Microsoft Windows [Version 6.1.7600]
    Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

    C:\Windows\system32>CD C:\Users\gurukripa\Documents\NetBeansProjects\I-ROOM\dist


    C:\Users\gurukripa\Documents\NetBeansProjects\I-ROOM\dist>java -jar iroom.jAR
    Unable to access jarfile iroom.jAR

    C:\Users\gurukripa\Documents\NetBeansProjects\I-ROOM\dist>java -jar I-ROOM.jar
    Exception in thread "main" java.lang.UnsupportedClassVersionError: i/room/Essent
    ials (Unsupported major.minor version 51.0)
            at java.lang.ClassLoader.defineClass0(Native Method)
            at java.lang.ClassLoader.defineClass(ClassLoader.java:539)
            at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:12
    3)
            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)

    C:\Users\gurukripa\Documents\NetBeansProjects\I-ROOM\dist>

I am using:

• Netbeans 7.0,
• JDK 1.7.0_02,
• JRE 7
• Windows 7 32-bit Home Premium

When I double-click on the jar nothing happens, but I can see javaaw is running in task manager. Is there a valid reason for this?

Answer 1

Your JAR was compiled with a different version of the JDK than the one you are trying to use to run it. Ensure that both Netbeans and command line are using the same version of the JDK.