从Netbeans清理并构建项目后，为什么我的jar文件无法执行？

Question

I followed some online tutorial and build a little GUI. I tried to make a jar file by clean and build project in the Netbeans, but the jar file doesn't let me open for some reason. Am i missing other stuff?

okay here is what happens after i type in java -jar GUI2.jar

Exception in thread "main" java.lang.UnsupportedClassVersionError: gui2/GUI2 : U nsupported major.minor version 51.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(Unknown Source) at java.lang.ClassLoader.defineClass(Unknown Source) at java.security.SecureClassLoader.defineClass(Unknown Source)at java.net.URLClassLoader.defineClass(Unknown Source) at java.net.URLClassLoader.access$000(Unknown Source) at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) Could not find the main class: gui2.GUI2. Program will exit

Answer 1

If you want to execute a JAR file, you can run from command line "java -jar yourJarFilePathHere".

Also, take a look at this SO post...

https://stackoverflow.com/a/5258323/1246574

Answer 2

Unsupported major.minor version 51.0

This tells that runtime environment doesn't support the format of class compiled

Either upgrade JRE to supported version or compile your source with runtime environment compatibility by adding -source switch

For netbeans: right click on project > properties > source select the source version compatible with your runtime version (java -version from terminal where you are running it) and rebuild the jar

Answer 3

The problem is that when you compile a java file it targets a certain version of Java (1.6, 1.7, etc). So if you compile your project for version 1.7, but on your computer you only have installed 1.6, it will give you this Unsupported major.minor version error when you try to run it. That just means there's a mismatch between the target version and the installed version.

The solution: check the Java version currently installed on your computer with java -version from the command line. I would just go ahead and update to be safe. Then check the target in your Netbeans settings (right click your project name -> Properties -> Sources -> Source/Binary format)