The mouseReleased callback must call a similar function in the button class for each instance.
The class will check if the mouseX/mouseY is within its surface (check against position and dimensions). If not, the event is ignored, otherwise, it is handled.

clickableObject[] clickables = new clickableObject[10]; // for example
boolean hitFound;

class clickable{
 float x1,y1,x2,y2;
 clickable(float _x1, float _y1, float _x2, float _y2){
   x1 = _x1;  y1 = _y1;  x2 = _x2;  y2 = _y2:
 }
 void mouseCheck(){
    if ((mouseX>=x1) && (mouseX<=x2) &&
       (mouseY>=y1) && (mouseY<=y2)){
     // handle your event, turn the button blue, whatever
     hitFound = true; // so the click won't go "through" to anything else
   }
 }
}

void mousePressed(){
 hitFound=false;
 for (int i=0; i< clickables.length; i++){
  if (!hitFound) clickables[i].mouseCheck();
 }
}

--Ben