Could not find or load main class (Windows 7 command line)

[jbean079]

Dear Forum members:

I have trouble to run .java file under command prompt in Windows 7.
JDK version: jdk1.7.0_02
When I typed in java MyFirstClass, I received following error message

C:\Users\admin121\workspace\helloworld\src\hellowo rld>java MyFirstClass
Error: Could not find or load main class MyFirstClass

I tried javac -cp option i received following error message

C:\Users\admin121\workspace\helloworld\src\hellowo rld>javac -cp MyFirstClass.java
javac: no source files
Error: Could not find or load main class MyFirstClass.java
Usage: javac <options> <source files>
use -help for a list of possible options

I use Eclipse run MyFirstClass.java it works fine.

• the .classpath file is inside a parent folder 'helloworld'.
• src folder inside parent 'helloworld' file contains another 'helloworld' folder.
• the child 'helloworld' folder has 2 files: MyFirsclass.java and MyFirstClass.class

when I run javac MyFirstclass.java in command prompt, the system generated MyFirstClass.class file

Path and CLASSPATH environment variable configuration
I edited the path environment variable by adding C:\Program Files\Java\JDK1.7.0_02\bin, then javac MyFirstClass.java worked.
I created CLASSPATH variable with value %JAVA_HOME%\jre\lib (I removed JAVA_HOME variable)
should I edit CLASSPATH variable by writing out full path name like C:\Program Files\Java\JDK1.7.0_02\jre\bin?

base on Setting the class path this link. it suggest using java -cp option for each individual application, so it won't affect other applications.



I would like to know which option is better: setting value for CLASSPATH variable or by using java cp <source file> option in the command prompt at run time?

I search the internet for the similar issues, but I haven't find the solution to my problems. Please give me some advises on how to make it work properly.

[Zigster]

I'm still very new to Java, but from the tutorials I did it said not to put .java after the file name when you are running the class file, and that's what worked for me. So: C:\Users\admin121\workspace\helloworld\src\hellowo rld>java MyFirstClass

[DarrylBurke]

I would like to know which option is better: setting value for CLASSPATH variable or by using java cp <source file> option in the command prompt at run time?

The second. But it's not <source file>, it's the package root(s) and jars.

db

[jbean079]

I'm still very new to Java, but from the tutorials I did it said not to put .java after the file name when you are running the class file, and that's what worked for me. So: C:\Users\admin121\workspace\helloworld\src\hellowo rld>java MyFirstClass

Thanks for the reply Zigster:

I had typo in the quoted text for error message. I didn't add .java when when using java MyFirstClass to run the program.
In my helloworld folder: I have MyFirstClass.class and MyFirstClass.java file

[jbean079]

The second. But it's not <source file>, it's the package root(s) and jars.

hello db:

Thanks for the reply. In my case, what is the package roots and jars for the MyFirstClass.java file?
Could you take a look at my original post and tell me what went wrong when I used javac -cp option?
Thanks for your help.

[Norm]

When you entered the command: java MyFirstClass
Where was the MyFirstClass.class file?
Was it in the same directory as where you issued the java command? Use the dir command to display the directory's contents.

[jbean079]

When you entered the command: java MyFirstClass
Where was the MyFirstClass.class file?
Was it in the same directory as where you issued the java command? Use the dir command to display the directory's contents.

Hello Norm:
Thanks for the reply. I initially create the workspace and the project by using Elipse.
Please help me to resolve the issue.

I copied and pasted MyFirstclass.class and MyFirstClass.java file into parent folder (helloworld) or \src folder and run the same
command I got same error message

Parent directory (helloworld) content

C:\Users\admin121\workspace\helloworld>dir
Volume in drive C has no label.
Volume Serial Number is 06A0-1962

Directory of C:\Users\admin121\workspace\helloworld

04/22/2012 08:42 AM <DIR> .
04/22/2012 08:42 AM <DIR> ..
02/07/2012 11:29 PM 301 .classpath
02/07/2012 11:29 PM 386 .project
02/07/2012 11:29 PM <DIR> .settings
04/15/2012 10:01 AM <DIR> bin
04/22/2012 08:42 AM 443 MyFirstClass.class
02/08/2012 12:10 AM 225 MyFirstClass.java
04/22/2012 08:30 AM <DIR> src
4 File(s) 1,355 bytes
5 Dir(s) 194,006,331,392 bytes free

in the \src directory I have another directory called helloworld

Directory of C:\Users\admin121\workspace\helloworld\src\hellowo rld

04/21/2012 08:12 AM <DIR> .
04/21/2012 08:12 AM <DIR> ..
04/23/2012 05:41 AM 443 MyFirstClass.class
02/08/2012 12:10 AM 225 MyFirstClass.java
2 File(s) 668 bytes
2 Dir(s) 194,006,310,912 bytes free

[Norm]

What happens when you use the java command in the same folder that has the class file?
Your last post does not show. Can you do a dir and then the java command in the same window?

[jbean079]

What happens when you use the java command in the same folder that has the class file?
Your last post does not show. Can you do a dir and then the java command in the same window?

Hello Norm:

Thanks for following up with me. Here is the copy for the command prompt. I hope this can help you identify the problem.

C:\Users\admin121\workspace\helloworld\src\hellowo rld>dir
Volume in drive C has no label.
Volume Serial Number is 06A0-1962

Directory of C:\Users\admin121\workspace\helloworld\src\hellowo rld

04/21/2012 08:12 AM <DIR> .
04/21/2012 08:12 AM <DIR> ..
04/23/2012 05:41 AM 443 MyFirstClass.class
02/08/2012 12:10 AM 225 MyFirstClass.java
2 File(s) 668 bytes
2 Dir(s) 194,522,427,392 bytes free

C:\Users\admin121\workspace\helloworld\src\hellowo rld>java MyFirstClass
Error: Could not find or load main class MyFirstClass

[Norm]

I am unable to create the condition that gives that error message.

[DarrylBurke]

1) Does MyFirstClass.java start with a package statement?

2) What is the result of entering "CLASSPATH" on the command line?

3) what happens if you give this command?

java -cp . MyFirstClass

db

[jbean079]

Hello db:
Thanks for the reply. I hope with forum member's help, i can solve this problem.

1) Does MyFirstClass.java start with a package statement?

I don't have a package statement within the MyFirstClass.java file

2) What is the result of entering "CLASSPATH" on the command line?

when I typed 'CLASSPATH' in command line I got following error message
C:\Users\admin121>echo %CLASSPATH%
C:\Program Files\Java\jdk1.7.0_02\jre\lib

C:\Users\admin121>CLASSPATH
'CLASSPATH' is not recognized as an internal or external command,
operable program or batch file.

3) what happens if you give this command?

java -cp . MyFirstClass

the command prompt gave me the following error message

C:\Users\admin121\workspace\helloworld\src\hellowo rld>java -cp . MyFirstClass
Exception in thread "main" java.lang.NoClassDefFoundError: MyFirstClass (wrong name: helloworld/MyFirstClass)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknow n Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(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)
at sun.launcher.LauncherHelper.checkAndLoadMain(Unkno wn Source)

[DarrylBurke]

Post the entire code of MyFirstClass.java. Don't leave out any lines.

db

[pbrockway2]

Follow the advice given in the Oracle link and seconded by db: Remove the CLASSPATH environment variable. Use -cp instead.

One effect of setting the CLASSPATH is that the java executable will attempt to use it and not the current directory when looking for the class you specify. It won't find it at the CLASSPATH location and that will lead to the "Could not find or load main class ..." which you mentioned in your first post.

"C:\Program Files\Java\jdk1.7.0_02\jre\lib" is a strange value for the CLASSPATH variable in any case. And was *not* suggested in that page to which you linked.

-----

Exception in thread "main" java.lang.NoClassDefFoundError: MyFirstClass (wrong name: helloworld/MyFirstClass)

This strongly suggests a package problem. Please post the contents of the MyFirstClass.java file.

[Norm]

java.lang.NoClassDefFoundError: MyFirstClass (wrong name: helloworld/MyFirstClass)

The class is in the helloworld package which changes the requirements for contents of the commandline.
The quick and easy fix is to remove the package helloworld; statement from the program and try again.

[jbean079]

The class is in the helloworld package which changes the requirements for contents of the commandline.
The quick and easy fix is to remove the package helloworld; statement from the program and try again.

Hello Norm, pbrockway2 and db:

I appreciate your guys' advises and step by step instruction to help me find the cause of the problem.
I removed the package statement (package helloworld;) in my code, then compile and run MyFirstClass.java. It worked like a charm:)

Here is my original code:

package helloworld; //trouble caused by the package statement

public class MyFirstClass 
{

	/**
	 * @param args
	 */
	public static void main(String[] args) 
	{
		// TODO Auto-generated method stub
        System.out.println("Hello Eclipse!");
	}

}

[Norm]

In post #12 you said: I don't have a package statement within the MyFirstClass.java file
Strange that you were able to remove something that was not there and have the code work.

[jbean079]

In post #12 you said: I don't have a package statement within the MyFirstClass.java file
Strange that you were able to remove something that was not there and have the code work.

Hello Norm:

My apology to you and other moderators. I didn't carefully check my code at the time. I could resolved the issue earlier if I read my code thoroughly.