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Singleton Instance

 
Rancher
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I'm putting this question here since it's a case of implementation rather than theory.
In the Singleton Creation Pattern there only ever exists a single instance of the object. My problem is that I want to model application properties as a Singleton (eg MyProperties.getProperty(xxx)) but also be able to have multiple version of the Properties so that each can control a different area.
To paraphrase, I want a single instance of a properties wrapper, but also be able to extend it so that I can have Application properties, Email Properties, etc etc and have the ability for some of them to be updated dynamically if the source file changes and others not...
So, as I was writing this I think I might be able to achieve this using a Properties Factory that DOES have instances but returns an instance based on what was asked for. If anyone wants to help flesh this out a bit I'd appreciate it. (No, it isn't an assignment )
Dave.
 
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It's interesting to note that the Singleton Pattern, as expressd in "Design Patterns" actually allows for multiple instances. Limiting the instaces to just one, is actually just a special case of limiting the number of instances to any particular number.
In your case, though, I really think that a factory approach is a much better solution. If you really insist, you can make your factory a singleton, but I'd try really hard to make it a regular constructed object and either pass it around or place it in a session or some other semi-persistent repository. Ill-considered over-use of the Singleton pattern is one of the most common maintainability problems I see these days.
 
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