1. //declare variables here
2.  
3. void setup(){
4.     //do setup stuff here
5.     //set size, initialize variables, run startup functions
6. }
7.  
8. void draw(){
9.     getVideo();
10.     detectCircles();
11. }
12.  
13. void getVideo(){
14.     //code to get a webcam signal here
15. }
16.  
17. void detectCircles(){
18.     //code to look for circles here
19.     if (foundCircle()){ //if there's a circle
20.         println(getDiameter()); //output the diameter
21.         println(getCoords()); //output the coordinates
22.     }
23. }
24.  
25. boolean foundCircle(){
26.     //evaluate whether a circle was found
27.     //if so...
28.     return true;
29.     //else...
30.     return false;
31. }
32.  
33. float getDiameter() {
34.     float d;
35.     //calculate the diameter here
36.     return d;
37. }
38.  
39. String getCoords(){
40.     float x,y;
41.     String result;
42.     //determine the coordinates here
43.     result = x + "," + y;
44.     return result;
45. }

thanks a lot for your fast response
Io non sono esperto con la programmazione
can you tell me the code for the detection of the spheres?
thanks

If you're looking at a picture, how would you as a human determine if there's a circle in it?  Pretend you have to explain it to somebody who doesn't know what the word circle means.

Hey,

Hough-Transform is a useful algorithm for circle-detection. Here is a nice explaination.
I once did an implementation for actionscript, but you can surely find some code for java if you search the web. I think opencv might be able to do this.