如何从类方法中访问常量

Question

I'm migrating a php application from procedural to oop.
I use a DEBUG constant to activate errors and warnings output (in fact, I have thee, every one makes the output more verbose.
But I can't find a way to access those constants from within a method.
The constants are defined before autoload in a separate file.

In the utility file I have

define('DEBUG', TRUE);

And inside a given method I tried to

if(!defined('DEBUG')) define('DEBUG', FALSE);

But I always end up with DEBUG=FALSE.
What am I doing wrong? I'm a total noob to oop, so be gentle please :-)

Clarification

Every class has his own file.
In any given script, the first thing I do is to include the utility file. The utility file is the one who defines DEBUG and has the _autoload function.

script_file.php
 includes utility_file.php
  defines DEBUG
  has _autoload function

Answer 1

darkphoenix was right, This wasn't an OOP problem. This was a NetBeans problem.
I'm using NetBeand and uploading the files to a remote server upon save. I've set the DEBUG constant to TRUE in the utility file and hit save on NetBeans, the save process (apparently) went without problems (no warnings or anything).
Big was my surprise when latter I logged in via SSH did a cat on the file. The file was never saved to the server. My local copy has my last edit, but the remote one doesn't...
Moral of the story: I hate you NetBeans