How to run Java from Firefox Extension using liveconnect?!

Question

Hi, I'm trying to run a very simple java program from a Firefox extension I'm making but I've run into a brickwall and just can't get it to work. I'm a complete beginner in java and don't know much javascript so I've copied and pasted code from around the net to get where I am now. I'm sure I'm just making some stupid error at some step.
In order to work out what I'm misunderstanding/doing wrong I'd be really grateful if someone could show me how to get it to work using a very basic example:
Say I have a .java file taken from the sun pages:
* The HelloWorldApp class implements an application that
* simply displays "Hello World!" to the standard output.
class HelloWorldApp {
    public static void main(String[] args) {
        System.out.println("Hello World!"); //Display the string.
}So I stick it into a jar using:
jar.exe cvfe HelloWorldApp.jar HelloWorldApp.class HelloWorldApp.class
I then place it directly on my C: drive.
In the javascript of my firefox extension I have code copied and pasted from https://developer.mozilla.org/en/Java_in_Firefox_Extensions:
var urlClasz = java.lang.Class.forName("java.net.URL");
var urlArray = java.lang.reflect.Array.newInstance(urlClasz,1);
urlArray[0] = new java.net.URL('file:///C:/HelloWorldApp.jar');
var cl = java.net.URLClassLoader.newInstance(urlArray);
var aClass = java.lang.Class.forName("HelloWorldApp", true, cl);
var aStaticMethod = aClass.getMethod("HelloWorldApp", []);
var greeting = aStaticMethod.invoke(null, []);This seems to start java but then only gives me the error:
"Error: uncaught exception: Error calling method on NPObject! [plugin exception: java.lang.ClassNotFoundException: HelloWorldApp]."
I would be infinitely grateful if someone could show me the code I would use in this situation to run the HelloWorldApp. If I could get it working in this basic situation I'm sure I could work it out from there.
Thank you very, very much!!

Answer 1

By the way, I answered just because nobody did and I have some experience with using java from mozilla javascript.
But I never played with Firefox extensions.
No problem baftos, I understand you might not have all the answers but you've helped loads so far, so thanks a lot! I've found it very difficult to find good documentation on this for a beginner like me.
Adding public did it (although I thought that I'd tried that, oops) so thanks again for that. I may have a couple of other questions just in case you happen to know the answer!
I'd like to send some string arguments to the method I really want to run eg:
public class HelloWorldApp {
public static void sayHello(String[] args)
{code}After googling .forName and .getMethod to see how to pass parameters I've added some code:
{code:java}
var strClass = java.lang.Class.forName("java.lang.String");
var parameters = java.lang.reflect.Array.newInstance(strClass,2);
parameters[0] ="My string argument";
parameters[1] ="3"; // etc...
var argHolder = java.lang.reflect.Array.newInstance(strClass,1);
argHolder[0] = strClass;
var aClass = java.lang.Class.forName("HelloWorldApp", true, cl);
var aStaticMethod = aClass.getMethod("sayHello", argHolder);
var greeting = aStaticMethod.invoke(null, parameters);
{code}What I thought I was doing was creating a java array: argHolder and putting the string class/object thingy?! in it so that getMethod would look for a method called "sayHello" which took a string array as an argument... but apparently not!
This brings me back to square one with a cannot find method with these arguments error:
"Error: uncaught exception: Error calling method on NPObject! [plugin exception: java.lang.IllegalArgumentException: No method found matching name getMethod and arguments [java.lang.String, [Ljava.lang.String;]]."
You don't happen to know how to do this as well do you?!
Edited by: mzatanoskas on Feb 13, 2009 1:40 PM