I run the following code in Eclipse IDE:

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

And it renders the expected output.

When getting into the command prompt (DOS) already in the directory, I type this

javac HelloWorld.java

And then this

java HelloWorld

And the output reads

Exception in thread "main" java.lang.NoClassDefFoundError: 
HelloWorld <wrong name:learning/HelloWorld>

With a whole lot more errors, learning being the name of my general package. What's wrong? I have installed Eclipse x86 SDK 4.2.0 together bit with the latest JRE and JDK both in 64 bit as well.