Thread: NoClassDefFound

I am writing a Java project, with public static void main in ClassMain class and somehow get this NoClassDefFoundError (before, evereything worked correctly).

java.lang.NoClassDefFoundError: ClassMain
Caused by: java.lang.ClassNotFoundException: ClassMain
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)
Exception in thread "main"

I found something at Bug ID: 6434149 (cl) ClassLoader.loadClass() throws java.lang.ClassNotFoundException: [Ljava.lang.String; in JDK 6.0 but I do not know where to change this -Dsun.lang.ClassLoader.allowArraySyntax=true I am using Eclipse.

Any help please?

How are you executing the java class? What command are you using?
Is there a class named ClassMain? Has it been successfully compiled and is there a ClassMain.class file where the java command can see it (ie its on the classpath)?

I have a class named ClassMain name in my project but it does not compile (folder "Bin" does not contain any of .class files)

You won't be able to execute the program without a .class file.

it does not compile

If there are errors, copy and paste the full text here.

This is complete code I am talking about (project also contains a heap of other classes, none of them containing main method.

import java.io.FileNotFoundException;
import java.io.IOException;
 
 
 
public class MainClass{
 
 public static void main(String[] args) throws IOException,FileNotFoundException,ClassNotFoundException{
 
 
 
		System.out.println("Does not work!!!");
	}}

2-3 days ago I had same problem Then I just put static void main into another class and it was then again ok. Today I have written some of documentation and created JavaDOC and after that (till now) this does not work. Putting static void main into another class also does not help.

Sorry, I was referring to the error message. Please copy and paste the full text of the error message here.

One observation:
java.lang.NoClassDefFoundError: ClassMain
vs
public class MainClass{

The class names shown are different.

That's just my typo (with ClassMain and MainClass (names are same)) Sorry for that.

Message in console is that one from my first post and it also shows one frame with name "Java Virtual Machine Launcher" and message Could not find main class: ClassMain Program will exit.

Where is the the file: ClassMain.class?
Open a comand prompt, change to the folder holding the ClassMain.class file and issue the command:
java ClassMain
This should start your program executing.
If not, copy and paste the contents of the screen here.
To copy the contents of the command prompt window:
Click on Icon in upper left corner
Select Edit
Select 'Select All' - The selection will show
Click in upper left again
Select Edit and click 'Copy'

Paste here.

As I have written previously, there is none ClassMain.class !!! I have just ClassMain.java written in eclipse editor and normally in project folder i have bin and src folders and bin is just empty

Then you must compile it to create a .class file.

If Eclipse hasn't compiled (aka built) the classes for you, go to Project->Build Automatically to let eclipse build it automatically for you. Alternatively, go to Project->Build Project. This should compile the classes for you.

That does not help Again "bin" folder is empty First time I got this problem I did not get solution (quickly) and I had to create new project and copy all classes to it and it started to work (no code change was done).
Now I am 100 % sure that it is not up to me It worked (showed GUI), then I just changed text written on one of JLabels and now I get this error Could not find the main class etc...

Can you successfully compile the program? Does it generate a .class file?

That is problem I think It does not compile I used this copeg's suggestion and no error message is shown when I select Project->Build Project and I check "bin" folder that normally contains .class files and it is empty Very strange

You need to find a forum for your IDE and ask them how to configure it.