C[omp]ute

From: "andrew cooke" <andrew@...>

Date: Fri, 3 Mar 2006 10:39:28 -0300 (CLST)

This Java ugliness turned up at work, but I don't see how to improve it.

We have are using a messaging system (Mule) that can make routing
decisions based on the message type (messages are POJOs).  Which is cool. 
We also have a need for a generic message:

public Message<E> {
  private E payload;
  public E getPayload() {return payload;}
  public void setPayload(E payoad) {this.paylod = payload;}
}

But Java erases generic types.  So this is sent to the messaging system as
a plain old Message.  Which means we can't route on the payload.  So we
end up writing a subclass:

public StringMessage exetends Message<String> {
  public String getString() {return getPayload();}
  public void setString(String string) {setPayload(string);}
}

Yuck.

Actually, writing that, I wonder what the point of the extra setters is. 
You already inherit a correctly typed getPaload and setPayload.  So it
seems to me that, apart from the slightly less informatitve method names,
the following is equivalent:

public StringMessage extends Message<String> {}

And that raises the question - why didn't Java do this to implement
generics?  It's what C++ templates do, and while there are problems,
they're not insurmountable, AFAIK.

Andrew