Ball[] balls = new Ball[10];

int tx, ty;
Ball selected;
 
void setup(){
  size(600,600);
  for(int i = 0; i < 10; i++){
    balls[i] = new Ball();
    registerDraw(balls[i]);
    registerMouseEvent(balls[i]);
  }
}
 
void draw(){
  background(0);
}
 
 
public class Ball{
  int x,y, radius, diameter;
  int fillCol, strokeCol;
  
  Ball(){
    int r,g,b;
    r = 128+(int)random(127);
    g = 128+(int)random(127);
    b = 128+(int)random(127);
    fillCol = color(r,g,b);
    strokeCol = color(r/2,g/2,b/2);
    x = 50 + (int)random(400);
    y = 50 + (int)random(400);
    diameter = 50 + (int)random(100);
    radius = diameter/2;
  }
  
  boolean isOver(int mx, int my){
    return (mx-x)*(mx-x) + (my-y)*(my-y) < radius*radius;
  }
  
  // This method is called automatically every loop
  // becasue we have registerDraw(this object)
  void draw(){
    ellipseMode(CENTER);
    fill(fillCol);
    stroke(strokeCol);
    strokeWeight(2);
    ellipse(x,y,diameter,diameter);
  }
  
  // This method is called automatically every loop
  // becasue we have registerMouseEvent(this object)
  void mouseEvent(MouseEvent event){
    if((selected == null && isOver(mouseX, mouseY)) 
                                      || selected == this){
      switch(event.getID()){
        case MouseEvent.MOUSE_PRESSED:
          selected = this;
          break;
        case MouseEvent.MOUSE_DRAGGED:
          x = x + mouseX - pmouseX;
          y = y + mouseY - pmouseY;
          break;
        case MouseEvent.MOUSE_RELEASED:
          selected = null;
          break;
      }
    }
  }
}