Program don't work

[baltimore]

Hi, I've looked around for a sample program and i found one which is supposed to print "I'm a sample program" on the screen. however when i launch the .jar it says that there is no main class definition, now i would add one myself but I'm new to java and have no clue what that is or where to add one, could someone help me with this? the code is below

//A Very Simple Example
class ExampleProgram {

   public static void main(String[] args){

        System.out.println("I'm a Simple Program");
   }
}

Thanks

[hardwired]

Setting an Application's Entry Point