Re: Design Patterns

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <>
Mon, 04 Feb 2013 21:41:18 -0500
On 2/4/2013 11:06 AM, Joerg Meier wrote:

On Sat, 2 Feb 2013 16:17:09 -0800 (PST), wrote:

I'm writing an application and I have the following problem.
When I write EventListeners I write them in seperate classes (and
seperate files) for reasons of clearity. But these event
listeners I want to modify other classes that aren't defined in
the EventListeners. They already exist in the main program.
The problem I have is how best to get these eventlisteners to
know of these classes (which are also in seperate files)? Up to
know I have used Singletons (I made the classes the event
listeners were to modify global) but this seems ugly. How are
java applications written to let the eventlisteners see the
classes they are to modify (sometimes these classes are seperate
application components in seperate files)?

While we are talking about design patterns, you should be aware that a lot
of people now consider Singletons an antipattern. Your usage of them
certainly sounds like the justly despised "global variable" replacement
many people abuse them for. Might be a good idea to reconsider that design.


I don't see Singleton as an anti-pattern.

But it is certainly bad design if Singleton is used
as global variable that all code is writing to and
reading from making it very hard to figure out
what is going on.

And the description could sound like this is
indeed the case.

I don't see a problem if it is well defined who
writes and who reads. Having a Singleton load
config information and expose readonly API
is fine.

I don't see a problem if usage is independent
of other usage. With a connection pool you don't
care who else is using the connection pool. With
a statistics collector you don't care who else is
updating statistics.


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