i'm working on a multy threading app in processing, this is my first result, but is real multythreading or i can obtain something more?

1. int threads = 2;  //numero di threads da creare
   int n = 10000;
   particle particles[] = new particle[n];
   
   worker process[] = new worker[threads];  //array di processi
   Thread threadProcess[] = new Thread[threads];  //array di thread contenente process
   
   void setup(){
     background(0);
     size(400,400);
     background(0);
     stroke(255);
     smooth();
     for (int i=0; i<n; i++){
       particles[i] = new particle();
     }
     //scorri i thread, e di da dove a dove calcolare (start, stop);
     for (int i=0, start = 0, stop = n/threads;  //inizializza variabili
                                             i<threads;  //condizione d'uscita
                                             i++, start+=stop){  //aggiorna variabili a ogni ciclo
       process[i] = new worker();
       process[i].start = start;
       process[i].stop = stop;
       stop += n/threads;
       threadProcess[i] = new Thread (process[i]);
     }
   }
   
   void draw(){
     background(0);
    
     for (int i=0; i<threads; i++){
       process[i].run();
     }
    
     for (int i=0; i<n; i++){
       particles[i].draw();
     }
     println(frameRate);
   }
   
   /*------------------------------*/
   class worker implements Runnable{
     int start, stop;
     void run(){  //metodo obbligatorio
       for (int i=start; i<stop || i<n; i++){//i<n evita di uscire dall'array particles[n]
         particles[i].update();
       }
     }
   }
   
   /*------------------------------*/
   class particle{
     PVector pos = new PVector(random(width),random(height));
     PVector vel = new PVector(random(-5,5), random(-5,5));
    
     void update(){
       if(pos.x>width || pos.x<0) vel.x*=-0.7;
       if(pos.y>height || pos.y<0) vel.y*=-0.7;
       pos.add(vel);
     }
     void draw(){
       point(pos.x,pos.y);
     }
   }
   

like the title, my question is:
what's the different between this code:

1. class system{
     //some code...
   }
   
   class start extends system{
     //some code...
   }
   
   class stop extends system{
     //some code...
   }
   
   class update extends system{
     //some code...
   }
   
   class draw extends system{
     //some code...
   }
   

and this?

1. class system{
     class start{
       //some code...
     }
     class stop{
       //some code...
     }
     class update{
       //some code...
     }
     class draw{
       //some code...
     }
   }
   

my question born from a totaly teorical point of view, thank's for your help.

Hi guys,
i'm understanding deeper the power of java, and after reading this page i've tryed something, but i encounter in a error. i think the code was good, but when i compile receive this error: "The costructor atoms(float,float,float,float) is undefined"
but is defined it in the atoms class!
PS: sometime it works until you saved the sketch, is it a bug?

1. int n = 10;
   atoms []h = new atoms[n];
   
   void setup() {
     size(300, 300);
     for (int i=0; i<n; i++){
       h[i] = new atoms(random(width), random(height), random(-5, 5), random(-5, 5));
     }
   }
   
   void draw() {
     background(0);
     for (int i=0; i<n; i++){
     h[i].update();
     h[i].display();
     }
   }
   
   class atom {//contiene le variabili degli atomi
     float px, py, vx, vy;
   }
   
   class atoms extends atom {//contiene funzioni degli atomi(utilizzando le variabili)
     atoms(float a, float b, float c, float d) {
       px = a;
       py = b;
       vx = c;
       vy = d;
     }
     void display() {
       point(px, py);
     }
     void update() {
       if (px+vx>width || px+vx<0)vx*=-1;
       if (py+vy>height || py+vy<0)vy*=-1;
       px+=vx;
       py+=vy;
     }
   }