instanciate an interface - alternatives?

From: Adi Schwarz (adolf.schwarz.news.01-04_at_gmx.at)
Date: 01/29/04 

Date: Thu, 29 Jan 2004 14:57:59 +0100

Hi,

I know that it is not possible to instanciate an interface. But are
there any workarounds?

I want to write a class that stores and manages certain objects. This
objects have to implement an interface called "SelfLoadable", that means
they can manage to load their information (from a file, database,
internet,...) themselves by providing a key that identifies the object
(e.g. primary key).

public interface SelfLoadable {
   public abstract void load(Object key);
}

Now my main class named ObjectCache shall contain a method named "get".
It shall look up if this object is stored in the cache, if not it shall
create it and automatically load its data:

   private Hashtable cache = new Hashtable();

   public SelfLoadable get(Object key) {
     SelfLoadable o;
     o = (SelfLoadable)cache.get(key);

     if (o == null) { //Object not stored?
       o = new SelfLoadable();
       o.load(key);
     }
     return o;
   }

new SelfLoadable(); does not work since it is an interface. But how do I
create the object if it is not stored in cache?

The idea is that I do not have to care about the cache - the get method
shall always return the object I request, no matter if the object is
cached or not.

I hope I could reduce the problem so far that it is understandable.

greets,

-adi

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