exception in thread "main" error

[ZeBula8]

i am brand new to java and i get this error at the command line with this code below -

i compiled into class and then try to run

***********************************************
c:\>javac GetPropertyDemo.java

c:\>java GetPropertyDemo
Exception in thread "main" java.lang.NoClassDefFoundError: GetPropertyDemo
************************************************

could someone explain to me why this is?

import java.lang.*;

class GetPropertyDemo {
	public static void main(String args[]) throws SecurityException {
		System.out.println ("OS Name: " + System.getProperty("os.name"));
		System.out.println ("OS Architecture: " + System.getProperty("os.arch"));
		System.out.println ("OS Version: " + System.getProperty("os.version"));
		System.out.println ("User: " + System.getProperty("user.name"));
		System.out.println ("Home Dir: " + System.getProperty("user.home"));
		System.out.println ("Java Version: " + System.getProperty ("java.version"));
		System.out.println ("Java Home: " + System.getProperty ("java.home"));
	}

}