Java wont open .class file

Question

ok i just started at this and found this web site http://java.sun.com/docs/books/tutorial/getStarted/cupojava/win32.html#1
i copyed exactly what he says to copy:
* The HelloWorldApp class implements an application that
* displays "Hello World!" to the standard output.
public class HelloWorldApp {
public static void main(String[] args) {
// Display "Hello World!"
System.out.println("Hello World!");
then put all that in notepad save it as "HelloWorldApp.java". i go to the msdos prompt type in javac HelloWorldApp.java it turns it in to a .class file and i type it
java HelloWorldApp and it gives me an error:
Exception in thread "main" java.lang.NoClassDefFoundError: helloworldapp (wrong
name: HelloWorldApp)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
What did I/He do wrong.

Answer 1

thanks it worked. can you tell my why?