Java Classpath Issues - will not run

Question

I'm learning how to run Java from the command line, and keep running into the same issue. The main() method I'm running is in bin/edu/cuny/util/ConvertTestVectors.class.

I set my directory to bin/cuny/. When I run > java -cp . ConvertTestVectors I get:

Error: Could not find or load main class ConvertTestVectors

When I run > java -cp . util/ConvertTestVectors I get:

Exception in thread "main" java.lang.NoClassDefFoundError: util/ConvertTestVectors (wrong name: edu/cuny/util/ConvertTestVectors)
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:791)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
        at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:480)

Could someone point me in the right direction? Thanks!

tcb · Accepted Answer · 2013-01-06 20:19:08Z

2

To run a main method of some java class you have to specify the fully qualified name of this class in the command line. For example, if you have in your source:

package edu.cuny.util;

class ConvertTestVectors {
    ...
    public static void main(String [] args) {
        ...
    }
    ...
}

then to run this main method you should use

java edu.cuny.util.ConvertTestVectors

If your package name is different, you should change the class name in command line accordingly.

Also, there is a CLASSPATH variable, which determines the location where java looks for classes. It should contain the directory where the root of your java packages in located (the parent directory of edu is case of the previous example). If it contains . then you can just change directory to that root directory and run java command.

The parts of a fully qualified class name are separated by dots (.) so you should not use slashes (/) in class name

answered Jan 6, 2013 at 20:19

tcb

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1 Comment

ldam Over a year ago

That's why the OP used -cp . ;)

ldam · Accepted Answer · 2013-01-06 20:00:25Z

1

cd bin/edu/cuny && java util.ConvertTestVectors

You have to use the full package name.

answered Jan 6, 2013 at 20:00

ldam

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5 Comments

Adam_G Over a year ago

Thanks. But that's what gives me the second error, the NoClassDefFoundError.

ldam Over a year ago

You said you got the second error from util/ConvertTestVectors, not util.ConvertTestVectors.

Adam_G Over a year ago

I changed the / to a . and it didn't matter.

ldam Over a year ago

What package is the class in then?

Adam_G Over a year ago

Got it! The other answer, which the user deleted, solved the problem. When I run java edu.cuny.util.ConvertTestVectors from bin it takes care of it. Thanks so much for your help, though!

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