Help me compile simple program

[richcash]

Well, I installed JDK 5.0 on my computer (and it took up a lot of space!) and then tried to test it out by writing this code :

code:

/**  * The HelloWorldApp class implements an application that  * simply prints "Hello World!" to standard output.  */ class HelloWorldApp {     public static void main(String[] args) {         System.out.println("Hello World!"); // Display the string.     } }

code from official java tutorials website
Then I went to command and was in the appropriate directory (because I saw the .txt file that I saved this code in) and I typed in javac filename.txt. It didn't recognize it and said javac was neither an internal or external command, etc.
My teacher said I have to download the JAR and the Application at drjava.org website, but can someone tell me if that's the problem and if I really need those before I go and download even more!

[richcash]

No edit or delete button! Sorry for the double post
I made a typo, just in case you get confused. I obviously type in javac filename.java (instead of .txt like I typed above) and it didn't recognize javac as a command as I said above.

[Andy]

you need to setup your environment variables

[richcash]

Thanks Andy, it works now, that was exactly the problem (I didn't read that page the first time I saw it!).