Looking for more resources about ArrayLists

Processing Beginners
41

Thanks for your questions.

Yeah, the boolean variable isDead is part of the class.

It signifies that the cell is dead. Initially isDead is false obviously.

  • isDead plays a role especially when we kill a big cell and replace it with 4 smaller ones (in the function mousePressed()). It is set to true to mark the old big cell as dead.

  • isDead is also used to remove old items from the ArrayList: When isDead it true, we remove (in a backwards for-loop in draw()). The code also works without the removing for-loop (maybe slower since we have more and more dead items in the ArrayList we have to skip).

Why does the code work without the removing for-loop? I’ll explain.

Details

Also for the (very short) time that items in the ArrayList exist that have isDead==true (or when we remove / comment out the removing for-loop), the class ignores dead objects:

  • Dead objects are not displayed anymore (in display()) and
  • they cannot be clicked. So onMouse() returns false when cell is dead. So it’s always saying, “No, I have not been pressed”.

Usage of return

These lines

    if (isDead) 
        return; //  the oldCell is DEAD and does not display

leave the function draw() before it really begins. But for the rest of the function we know: the cell is alive.

Alternatively you could say if( ! isDead) {.........} and put the entire content of the function in the if clause { … }. (Which would give you a code less clear.)

Usage in the function onMouse()

Similarly:

boolean onMouse() { 
    if (isDead) // When TRUE return FALSE state! Yes! Cell is not clicked by mouse (or pretends not to be)
       return false; // leave with false (mouse is never recognized on a dead cell)

So, when the cell is dead, we leave the function fast - with false.
This means a dead cell can never say, “the mouse has been clicked on me”.

  • Which is good because otherwise a dead cell could generate 4 children again and again. Not good.

The further lines of onMouse()

Nothing much about.

Now we read this in onMouse():

   // this can return true or false: // I'm not sure what this means? Or why true or false is okay
    return 
      mouseX>x   &&
      mouseX<x+w &&
      mouseY>y   &&
      mouseY<y+w;
  }//method

Well, this just means:

  • return true when mouse is inside and
  • false when mouse is not inside.

It’s a short form of this long form:

  if  ( mouseX>x   &&
      mouseX<x+w &&
      mouseY>y   &&
      mouseY<y+w) 
            return true;    // mouse was inside cell 
            else return false;     // mouse was NOT inside cell

In the short form we just return the result
of this condition directly:

    ( mouseX>x   &&
      mouseX<x+w &&
      mouseY>y   &&
      mouseY<y+w)

which is doing the same as the long form.

I hope this helps!

Chrisir

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