Button[] buttons = new Button[6];

void setup() {
  size (600, 400);
  smooth();
 
  for (int i = 0; i < buttons.length; i++) {
   buttons[i] = new Button(i*100+25, height/2-25, 50, 50); 
  }
}

void draw() {
  background(255);
  //show all buttons
  for (int i = 0; i < buttons.length; i++) {
  buttons[i].display();
}
}

void mousePressed() {
  // When the mouse is pressed, we must check every single button
  for (int i = 0; i < buttons.length; i++) {
    buttons[i].click(mouseX,mouseY); 
  }
}