int numBalls = 10;  // how many balls do we want?
Ball[] myBalls = new Ball[numBalls];  // declare and assign an array of Balls 
                                      // (this is basically reserves enough space
                                      // for a bunch of Balls... but doesn't really
                                      // CREATE them yet)
                                      

void setup(){

  frameRate(60);  // 60fps
  size(480,360);  // 640x480 window
  for(int i=0;i<numBalls;i++){  //count from 0 to numBalls-1
    myBalls[i] = new Ball();    //actually CREATE a new Ball Object.
    myBalls[i].x=random(width);  //give this Ball's x position (x) a random number between 0 and 640
    myBalls[i].y = random(height);  //give this Ball's y position (y) a random number between 0 and 480
    myBalls[i].vX=random(4)-2;  //give this Ball's horizontal velocity (vX) a random number between -2 and +2
    myBalls[i].vY = random(4)-2;  //give this Ball's vertical velocity (vY) a random number between -2 and +2
    myBalls[i].myColor = color(random(255),random(255),random(255));  // give this Ball a random color (assigning the myColor variable inside of this particular Ball)
  } 
    background(0);  // black background
}
void draw(){

  for(int i=0;i<numBalls;i++){  // count from 0 to numBalls-1
    myBalls[i].runMe();   // call this Ball's runMe(); function (open that box!)
  }
}

class Ball{  // declare the Ball class
  float x;  // declare enough space for floats x,y,vX,vY
  float y;
  float vX;
  float vY;


  color myColor;  // declare enough space for a color variable called myColor

  void runMe(){  // declaring and assigning the runMe() function. It takes nothing and returns nothing
    if(x>width || x<0){  // if this ball hits the left or right walls
      vX*=-1;   // reverse the horizontal velocity
    }
    if(y>height || y<0){  // if this ball hits the top or bottom
      vY*=-1; // reverse the vertical velocity
    }

    x+=vX;  // update the horizontal position based on the horizontal velocity
    y+=vY;  // update the vertical position based on the vertical velocity
    drawMe();  // call this Ball's drawMe(); function (open that box)
  }
  void drawMe(){  //declare this Ball's drawMe(); function. It takes nothing, and returns nothing
    noStroke();  // no outline
    fill(myColor);  // set the fill color to this Ball's myColor variable
    ellipse(x,y,10,10);  // draw a 10x10 ellipse at coordinates x,y
  } 
};