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"Could not find or load main class" Error while running java program using cmd prompt


Question

I am running a simple "HelloWorld" Program. I get this error in the command prompt:

Could not find or load main class HelloWorld.

I have set the CLASSPATH and PATH variable in the system. In the cmd prompt, I am running from the directory where I have saved HelloWorld program. I can see the class name and the file name are same and also .class file created in the same directory. What else could be the problem?

My sample program looks like this:

package org.tij.exercises;
public class HelloWorld {
  public static void main(String[] args) {
    // TODO Auto-generated method stub
    System.out.println("Hello World!!");
  }
}
2015/12/10
1
33
12/10/2015 10:35:23 PM


What's your CLASSPATH value?

It may look like this:

 .;%JAVA_HOME%\lib\dt.jar;%JAVA_HOME%\lib\tools.jar 

I guess your value does not contain this .;.

So, ADD IT .
When you done , restart CMD

That may works.


For example the file HelloWorld.java is in path: D:\myjavatest\org\yz\test and its package is: org.yz.test.

Now, you're in path D:\myjavatest\ on the CMD line.
Type this to compile it:

javac org/yz/test/HelloWorld.java

Then, type this to run it:

java org.yz.test.HelloWorld

You may get what you want.

2015/12/10

I removed bin from the CLASSPATH. I found out that I was executing the java command from the directory where the HelloWorld.java is located, i.e.:

C:\Users\xyz\Documents\Java\javastudy\src\org\tij\exercises>java HelloWorld

So I moved back to the main directory and executed:

java org.tij.exercises.HelloWorld

and it worked, i.e.:

C:\Users\xyz\Documents\Java\javastudy\src>java org.tij.exercises.HelloWorld

Hello World!!

2014/10/30

Since you're running it from command prompt, you need to make sure your classpath is correct. If you set it already, you need to restart your terminal to re-load your system variables.

If -classpath and -cp are not used and CLASSPATH is not set, the current directory is used (.), however when running .class files, you need to be in the folder which consist Java package name folders.

So having the .class file in ./target/classes/com/foo/app/App.class, you've the following possibilities:

java -cp target/classes com.foo.app.App
CLASSPATH=target/classes java com.foo.app.App
cd target/classes && java com.foo.app.App

You can check your classpath, by printing CLASSPATH variable:

  • Linux: echo $CLASSPATH
  • Windows: echo %CLASSPATH%

which has entries separated by :.

See also: How do I run Java .class files?

2017/05/23

I had the same problem, mine was a little different though I did not have a package name. My problem was the Class Path for example:

C:\Java Example>java -cp . HelloWorld 

The -cp option for Java and from what I can tell from my experience (not much) but I encountered the error about 20 times trying different methods and until I declared the class Path I was receiving the same error. Vishrant was correct in stating that . represents current directory.

If you need more information about the java options enter java -? or java -help I think the options are not optional.

I just did some more research I found a website that goes into detail about CLASSPATH. The CLASSPATH must be set as an environment variable; to the current directory <.>. You can set it from the command line in windows:

// Set CLASSPATH to the current directory '.'
prompt> set CLASSPATH=.

When you add a new environment setting you need to reboot before enabling the variable. But from the command prompt you can set it. It also can be set like I mentioned at the beginning. For more info, and if your using a different OS, check: Environment Variables.

2015/12/10

One reason for this error might be

Could not find or load main class <class name>

Maybe you use your class name as different name and save the class name with another name you can save a java source file name by another name than class name. For example:

class A{
    public static void main(String args[]) {
        System.out.println("Hello world");
    }
}

you can save as Hello.java but,

To Compile : javac Hello.java

This will auto generate A.class file at same location.

Now To Run        : java A

2016/06/23