Get vs set

Question

Hi guys, wondering about the title heh?
Well, I have been wondering about what would be the best way to access global variable.
Let's take for instance the case of a multi editor IDE like Eclipse.
an action occurs which is supposed to do some work on the current Editor. How does the action get a reference to the currently active editor?
2 ways: get or set.
get:
you actively get the reference with some kind of mechanism. (for example a variable singleton)
pros: minimal space (one reference), editor change takes O(1) in time,
cons: a fetch every time the variable is used, need for a supplying mechanism(singleton )
Danger that developer mis-read the specification and creates a local copy received by the "get" mechanism. (if anyone remember my post about destroying object /setting an object to null see http://forum.java.sun.com/thread.jsp?forum=31&thread=470148 )
set :
the reference is there. no other worries
pros: direct use possible
cons: space O(n), editor change O(n); n = number of users for editors
Event channel like mechanism to maintain the list of users and propagate editor changes.
Which one would you use?
I like "get" better.
NOTE: In Eclipse they are using "set"

Answer 1

It depends on your objectives and how often the active
dwg changes.
the set method is kind of like an observer and you may
end up cycling through several receivers each time the
active editor changes. Not a good idea because it can
slow down if you do too many things that way. I
prefer to give data only to those that immediately
need it, especially when that data will change.
Also you should know eclipse will return null for
certain editParts if the request is not inside the GUI
thread. In this case, how would the set method work?I'm a real newb in programming eclipse, doing some learning right now. Actually that's why I came up with this post. Because in Eclipse, IActionDelegate classes use the "set" method, i.e they are feeded with selection changes.
Eclipse returns null for some EditorPart ? hmm I don't see. What I'm referring to is this:
http://help.eclipse.org/help20/content/help:/org.eclipse.platform.doc.isv/reference/api/org/eclipse/ui/IEditorActionDelegate.html
If IEditorPart is null, well you do the same thing as if you have to "get" IEditorPart yourself.
"Get" method would do something like
IEditorPart iep = ActiveEditorSupplier.getActiveEditor();
if(iep == null)
  //do stuffWith the set method you only do
if(_currentEditor == null)
//do stuff
because you already have done
setActiveEditor(IAction action, IEditorPart targetEditor)  {
_currentEditor = targetEditor;
}