How to declare class variable with generic parameters?

Question

I've got a class that declares a type parameter T. I know how to declare a static method, but this doesn't work for a static variable:
public class Test< T >
    * Map of String to instances of T.
    * error: '(' expected (pointing to =)
    * <identifier> expected (pointing to () )
   private final static < T > Map< String, T > MAP = new HashMap< String, T >();
    * Get instance of type T associated with the given key.
   public final static < T > T getType( String key )
      return MAP.get( key );
}Edited by: 845859 on Mar 20, 2011 11:46 AM

Answer 1

jveritas wrote:
I'm trying to create a generic polymorphic Factory class that contains boilerplate code.
I don't want to have to rewrite the registration code every time I have a different return type and parameter.I haven't seen a case yet where that is reasonable.
If you have hundreds of factories then something is wrong with your code, design and architecture.
If you have a factory which requires large number of a varying input types (producing different types) then something is probably wrong with your code and design.
A reasonable factory usage is one where you have say 20 classes to be created and you need to add a new class every 3 months. Along with additional functionality represented by the class itself and perhaps variances in usage. Thus adding about 3 lines of code to one class is trivial. Conversely if you have hundreds of classes to be created by the factory and you are adding them daily then it is likely that
1. Something is wrong with the architecture which requires a new class every day.
2. You should be using a dynamic mechanism for creation rather than static because you can't roll out a static update that often.
More than that the idiom that leads to factory creation is different for each factory. A factory that creates a database connection is substantially different than the one used in dynamic rules logic processing. A generic version will not be suitable for both.
Actualy the only case I know of where such a factory might be seem to be a 'good' idea is where someone has gotten it into their head that every class should be represented by an interface and every class created by a factory (its own factory.) And of course that is flawed.