This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
I am putting together an abstract Singelton, that will then have implementing classes. These classes should only need to override one method(Hence the Template Method) so that it all works for the specific implementation type.
So I have this abstract class
And here is an implementation class
Forget about the implementation of the loadData method, it is using Hibernate to do a search for me.
But notice the static initializer.
OK, so you might guess what I am trying to do, but I am having no luck. I am just missing something that probably is pretty easy.
I am trying to make a call to getInstance of the object, and it will return the Singleton instance. Now the class that is calling getInstance is doing so through Reflection because that class only knows its type as the abstract class type.
Here is my CacheFactory that will either return an instance of that type that exists in a Map it has, or will create a new one and add it to the Map.
The problem right now is that the loadLookup method calling the getInstance static method is returning null.
I obviously want to make sure that when you call getInstance on any type of AbstractLookup and there is no instance of that type yet, that it will create one, and call loadData().
Even with it changed to a static block it won't work. The problem here is the DefaultLookup class is never loaded, the only method called belongs to AbstractLookup. Even it were loaded there's still a fatal flaw in the design: each new class loaded uses the same static variable.
I believe you'll need to create a registry or make getInstance() abstract and move the static variable to the implementing class.