Question

This concerns an attempt to run a network application. The code compiles correctly, however upon trying to run with “java SendMail” java returns :

C:\Butte>java SendMail
Exception in thread "main" java.lang.NoClassDefFoundError: SendMail (wrong name:
 je3/net/SendMail)
        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: SendMail.  Program will exit.

Is this a trivial configuration problem. I have a Java package recent enough to support other networking code. The source code is :

package je3.net;
import java.io.*;
import java.net.*;

/**
 * this software sends e-mail via a mailto : url
 */

public class SendMail {
    public static void main(String[] args) {
        // --- SNIP ----
    }
}

Thank you very much,

Joel

Answer 1

Your class is in a package je3.net, so you need to run it as:

java je3.net.SendMail

However, it sounds like you probably need to compile it differently too – as that will look for je3\net\SendMail.class as a filename. Basically your source and output should match the package structure you declare.

You don’t have to do it for the source – you could just write:

javac -d . SendMail.java
java je3.net.SendMail

as the -d . part will make javac create the right directory structure for you. However, I’d personally move SendMail.java to a je3\net directory.