macOS Running Java program from command line

[naples98]

I usually use NetBeans to program in Java but wanted to try to compile and run from the command line. I wrote a simple Hello World program (Main.java) and compiled it from the command line (javac Main.java) with no problem but when I try to run it from the local directory using

java Main

I get the following error.

Exception in thread "main" java.lang.NoClassDefFoundError: Main (wrong name: helloworld/Main)
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
	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$1.run(URLClassLoader.java:197)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:248)

Any ideas how I can fix this? I've looked around quite a bit but most suggestions haven't worked for me. I'm working on 10.6.6.

 

[lee1210]

Did you put your class in a package? If so, do you have the directory structure setup to match this package name?

-Lee

 

[jiminaus]

Try not going into the helloworld directory, but staying in helloworld's parent directory. And then try this:

java helloworld.Main

 

[naples98]

Did you but your class in a package? If so, do you have the directory structure setup to match this package name?

-Lee

I just wrote the program in NetBeans with a package name of helloworld. I went to the directory (~/NetBeansProjects/HelloWorld/src/helloworld) where Main.java was located and compiled there. Running it from that local directory did not work.

Just to try, I removed the package name and relocated Main.java to ~ which compiled and ran fine.

 

[naples98]

Try not going into the helloworld directory, but staying in helloworld's parent directory. And then try this:

java helloworld.Main

That worked. I guess I was trying to execute it from the wrong directory.

Thanks!

 

[ulbador]

Directories don't really matter in Java in the conventional sense. What matters is the directory that has the main method is somewhere in the class path.