Re: Help with an arraylist of subclass using generics

From:

Mark Space <markspace@sbc.global.net>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 21 May 2009 10:06:06 -0700

Message-ID:

<aSfRl.30228$Ws1.5671@nlpi064.nbdc.sbc.com>

Alessandro wrote:

Iterator<? extends RicDataElement> iter1 = buffer.iterator();

How about just:

Iterator<RichDataElement> iter1 = buffer.iterator();

  if(iter1.next() instanceof RicDataCrossElement){
      RicDataCrossElement crossElm=
          (RicDataCrossElement )iter1.next();

"instanceof" is used for evil here, but I understand what you are trying
to do. If there's a way to use polymorphism to accomplish this, I
encourage you to do so.

Let's say you have an existing class RichDataElement that you don't have
source access to. What about making some sort of wrapper for it?

class MyRdeWrapper {
   RichDataElement r;
   MyRdeWrapper( RichDataElement r ) {
     this.r = r;
   }
   // polymorphic methods go here...
}

Now you can wrap RichDataElements (and children) in this class and you
can delegate evil un-polymorphic stuff to the wrapper class, thus
cleaning up your higher level code. Depending on the structure of the
code, it may not buy you anything, but I thought I'd at least mention
this idea.