I have never used the Callable interface but a litte research shows using it is not that simple.

Do you need the StartManager class what is wrong with

1. void keyPressed() {
2.   if (keyCode==69)  {
3.     create();
4.   }
   
5. }

Many thanks for your answer Quarks!

There are several ways to do this, starting by using non static things: if you put a static method in a static class in Processing, you can as well make the method as a global function of your sketch, there is no conceptual difference, actually...

If you really want to go the way you show, instead of passing a generic PApplet instance, pass the instance of your sketch: if you name it SketchName, for example, declare:

1. static class StartManager {  
   
2.   static void startOnKeyPress(SketchName context)  {
3.    if (context.keyCode==69)  {
4.     //here is where I don't know how to call to create of the main file
5.     context.create();
6.    } 
7.   }
8. }

Hello PhilHo:

You can also use Reflection, which is quite useful when handling stuff like calbacks. I personally try to avoid using it. Instead I would rather use an Interface or go with something like PhiLho suggested, if the desired method in your main class. With that said, here is a sample code to demonstrate a simple callback. Please take a look at Reflection documentation for more advanced stuff.

I agree with m.peres. Reflection can be useful, but the more canonical way to do such thing in Java is to use interfaces. With the added advantage, over reflection, to work in JavaScript mode!

" more specialised"
Yes. Java doesn't know a create() method for PApplet, but know it exists for SketchName. Of course, the keyCode field exists for both classes.

" separate a little bit the responsibilities"
Yes, I understood that, but it is a bit over-engineered for most Processing sketches.
Java isn't as dynamic as JavaScript (a good thing, actually), so sometime you have to shake off the JS way of thinking and work more in Java mode (or in Processing mode, more relaxed).