Hi guys and gals,

This is a pretty basic question, but I am trying to make an app that has a series of "balls" that bounce around on the screen and when they approach squares on the screen, the ball will turn red.

However, I don't know how to talk to just one instance or a particular instance of a class. It seems like it should be so very easy but I am unable to figure it out. I tried this.fill() but that didn't work.

Thanks!

1. int nBalls = 12;
   Ball balls[] = new Ball[nBalls];
   int nSquares = 5;
   Square squares[] = new Square[nSquares];
   
   void setup(){
     size (500, 500);
     for (int i=0; i<nSquares; i++) {
       squares[i] = new Square((i*100)+50,height/2);
     }
      for (int i=0; i<nBalls; i++) {
       balls[i] = new Ball(random(0,width),random(0,height));
     }
   }
   
   void draw(){
     background(0);
     for (int i=0; i<nSquares; i++) {
       squares[i].update();
       squares[i].draw();   
     }//end for i
   
     for (int i=0; i<nBalls; i++) {
       balls[i].update();
       balls[i].draw();
        for(int j=0; j<nSquares; j++) {
           if(dist(balls[i].x, balls[i].y, squares[j].x,squares[j].y) < 25) {
               this.fill(255,0,0);
           }
          }
     }
   
   }//end draw
   
   //define Square class
       class Square{
         float x;
         float y;
        
         Square(float xPos, float yPos){
            this.x = xPos;
            this.y = yPos;
           
         }
        
        void draw(){
            rectMode(CENTER);
            rect(this.x,this.y,50,50);
        }
       
        void update(){
           
        }
    }// end square class
    
   
   //define Ball class
      class Ball {
        float speed;
         float x;
         float y;
         float xSpeed;
         float ySpeed;
        
         Ball(float xPos, float yPos){
           this.x = xPos;
           this.y = yPos;
           speed = random(.15, .75);
           this.xSpeed = speed;
           this.ySpeed = speed;
         }
       void draw(){
           ellipse(this.x,this.y,25,25);
       } 
       void update() {
       if(this.x < 0){
         this.x = 0;
         this.xSpeed *= -1;
       }
       if(this.x > width) {
         this.x = width;
         this.xSpeed *= -1;
       }
   
       if(this.y < 0){
         this.y = 0;
         this.ySpeed *= -1;
       }
       if(this.y > height) {
         this.y = height;
         this.ySpeed *= -1;
       }
      
       this.x +=xSpeed;
       this.y +=ySpeed;
     }
      }