I've been toying around with the excellent controlP5 library for some time now, but have come to the conclusion that I want to create my own gui elements.

I've built upon the Button examples and created a small sketch:

Code:

ArrayList buttons = new ArrayList();

boolean locked = false;

color c = color(0,0,0);

void setup() {
  size(400,400);
  background(0);

  buttons.add( new Button(80, 100, 100, 20) );  
  buttons.add( new Button(220, 100, 100, 20) );
} 

void draw() {

  background(c);

  // draw buttons
  if (buttons.size() > 0) {
    for (int i=0; i < buttons.size(); i++) {
	Button b = (Button) buttons.get(i);
	b.display();
	b.update();
    }
  }

  // how can I call randomBG() using the left button?
  //randomBG();
  
  // how can I call blackBG() using the right button?
  //blackBG();

}

void whiteBG() {
  c = color(255,255,255);
}

void blackBG() {
  c = color(0,0,0);
}



// Button
class Button {

  int x, y;
  int w, h;
  color basecolor, highlightcolor;
  color currentcolor;
  boolean over = false;
  boolean pressed = false;   

  Button (int _x, int _y, int _w, int _h) {    
    x = _x;
    y = _y;
    w = _w;
    h = _h;

    basecolor = color(153, 153, 153);
    highlightcolor = color(102, 102, 102);
    currentcolor = basecolor;     
  }

  void display() 
  {
    noStroke();
    fill(currentcolor);
    rect(x, y, w, h);
  }


  void update() 
  {
    if(over()) {
	currentcolor = highlightcolor;
    } 
    else {
	currentcolor = basecolor;
    }
  }

  boolean over() 
  {
    if( overRect(x, y, w, h) ) {
	over = true;
	return true;
    } 
    else {
	over = false;
	return false;
    }
  }


  boolean pressed() 
  {
    if(over) {
	locked = true;
	return true;
    } 
    else {
	locked = false;
	return false;
    }    
  }

  boolean overRect(int x, int y, int width, int height) {
    if (mouseX >= x && mouseX <= x+width && 
	mouseY >= y && mouseY <= y+height) {
	return true;
    } 
    else {
	return false;
    }
  }
}

 

I know the above problem is a simple task that could be solved differently, but I want to try the most elegant way using event listeners. Unfortunately, even after reading through the Java Tutorials on this topic I haven't managed to wrap my head around the concept of listeners.
So far I've learned it's about implementing and adding ActionListerens, but I'm afraid I have no clue where to start and place these things in my code.

Does anyone have a hint on how to I should begin to rewrite the code

Thanks so much.
Greg