Question

I am trying to run a class, but I get the following error:

java.lang.NoClassDefFoundError: MyClass
Caused by: java.lang.ClassNotFoundException: MyClass
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
 Exception in thread "main" 

It happens, although the main method is in MyClass and I run directly this class.
Why is this class not found, although I launch the program from it?

Here is some code:

public class MyClass extends A implements B{
public MyClass() throws Exception {
//make some initializations
}
public static void main(final String[] args) throws Exception {
MyClass myClass = new MyClass();
//do stuff with myClass
}
}

PS: I am using Eclipse Indigo.

EDIT
I have run the class in the Command Line twice:

D:\Eclipse JEE\Workspace2\Example\target\classes\com\example\main>java com.example.main.MyClass
Exception in thread "main" java.lang.NoClassDefFoundError: com/example/main/MyClass
Caused by: java.lang.ClassNotFoundException: com.example.main.MyClass
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class: com.example.main.MyClass.  Program will exit.

D:\Eclipse JEE\Workspace2\Example\target\classes\com\example\main>java GeoDAOImpl
Exception in thread "main" java.lang.NoClassDefFoundError: MyClass(wrong name: com/example/main/MyClass)
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
    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$1.run(URLClassLoader.java:197)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class: MyClass.  Program will exit.

Answer 1

You haven’t really given us enough information to say for sure, but my guess is that either:

• You’re not giving the right fully-qualified class name
• Your class isn’t on the classpath

For an example of the first case, if your code looks like this:

package foo;

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

Then you should be running:

java foo.MyClass

EDIT: With the extra information provided, I suspect I know what’s happened. I suspect the class was created not in a package, and a Run Configuration was created which just runs MyClass. It’s now been moved into com.example.main, but without the Run Configuration being updated.

Go into the Run Configuration editor (click on the dropdown next to the “run” button, and select Run Configurations…) and find “MyClass”, then check which class is going to be run, and edit it to put the right package name in.