Exception in thread "main" java.lang.NoClassDefFoundError:

Here is my code.

import java.io.*;
class Ex13{
    public static void main(String args[]) throws IOException{
        BufferedReader keyboard = new BufferedReader (new InputStreamReader(System.in));
       
        String input;
        int num = 0;
        int sum = 0;
       
        do {
        System.out.print("Enter a positive number: ");
        input = keyboard.readLine();
        num = Integer.parseInt(input);
       
        if ( num > 0)
            sum += num;
           
        }while (num > 0);
    System.out.println(sum);
    }
}

Compiling with javac hh.java was fine but somehow i got this error while run as java hh

Exception in thread "main" java.lang.NoClassDefFoundError: hh
   at gnu.j
ava.lang.MainThread.run(MainThread.java:102)
Caused by: java.lang.ClassNotFoundException: hh not found in gnu.gcj.runtime.SystemClassLoader{urls=[file:./], parent=gnu.gcj.runtime.ExtensionClassLoader{urls=[], parent=null}}
   at java.net.URLClassLoader.findClass(URLClassLoader.java:529)
   at gnu.gcj.runtime.SystemClassLoader.findClass(natSystemClassLoader.cc:27)
   at java.lang.ClassLoader.loadClass(ClassLoader.java:442)
   at java.lang.ClassLoader.loadClass(ClassLoader.java:377)
   at gnu.java.lang.MainThread.run(MainThread.java:98)

Hmmmm.. what went wrong? How do i fix it??

The class containing main function needs to be public

hmmm, thank you. After i change the java file name same as the public class, it works.