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  Singleton with generics - howto?  (Read 3433 times)
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Offline Bombadil

Senior Devvie

« Posted 2004-10-14 16:23:46 »

Which is the best way to use generics to write an abstract base class or an Interface for a Singleton?

I've many lazy created singletons in my code. Lazy means they create themself when the first user class declares the singleton class. It looks like this:
public class TheSingelton 
  private static TheSingelton sInstance = new TheSingelton();

  private TheSingelton()

  public static TheSingelton getInstance()  {
    return sInstance;

The con is that for every class which wants to be a Singleton it has to double these lines with its own type.
In C++ I used to use templates for these kind of things. I guess with generics we finally can have a real Singleton base abstract class or Interface in Java, too?
(I'd prefer an abstract class because even the sInstance shall be inside the base class, not in the derivate.)
Offline Bombadil

Senior Devvie

« Reply #1 - Posted 2004-10-14 17:06:58 »

That's exactly the error I run into with my silly-dilly Tiger implementation of a Singleton. I'm still too much in C++ templates (which Java generics are not)...

Btw did you ever visit a Java house? Ie a restaurant with Javanese food. Excellent, I can say... :-)
Offline jherber

Junior Devvie

Java games rock!

« Reply #2 - Posted 2004-10-21 23:25:19 »

another possibility is to not use inheritence/generics to abstract.  the gang of four's book "design pattern" usually recommends this method of abstraction.  for example, you could have a singleton that can be used to register other instances as singletons.  if you decide to register your singleton's by type, then you are using the concepts of a "flattened" version of  sun's beancontext.  if you register by string name then you have built a nameservice.
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