GradeBook displayMessage error

Question

I am using jdk.5.0_18 but still I am getting the error that GradeBook class symbol not found in this simple code.
public class DataGradeBook{
  public static void main(String args []){
    GradeBook xGradeBook = new GradeBook();
    xGradeBook.displayMessage();
}

Answer 1

"My fridge is broken."
"Try plugging it in."
"Oh, don't worry... It's a Kelvinator."
"WTF?"
You need to start communicating much more clearly or nobody will bother to help you. It's up to you.
* Don't even talk to me until you've:
    (a) [googled it|http://www.google.com.au/] and
    (b) looked it up in [Sun's Java Tutorials|http://java.sun.com/docs/books/tutorial/] and
    (c) read the relevant section of the [API Docs|http://java.sun.com/javase/6/docs/api/index-files/index-1.html] and maybe even
    (d) referred to the JLS (for "advanced" questions).
* [Good questions|http://www.catb.org/~esr/faqs/smart-questions.html#intro] get better Answers. It's a fact. Trust me on this one.
    - Lots of regulars on these forums simply don't read badly written questions. It's just too frustrating.
      - FFS spare us the SMS and L33t speak! Pull your pants up, and get a hair cut!
    - Often you discover your own mistake whilst forming a "Good question".
    - Many of the regulars on these forums will bend over backwards to help with a "Good question",
      especially to a nuggetty problem, because they're interested in the answer.