Re: A filtered iteration over a collection: current idiom?

From:
Jean-Baptiste Nizet <jnizetNOSPAM@NOSPAMfree.fr>
Newsgroups:
comp.lang.java.programmer
Date:
Sat, 18 Sep 2010 18:11:35 +0200
Message-ID:
<4c94e4cb$0$28687$426a74cc@news.free.fr>
Le 18/09/2010 16:36, Simon Brooke a ??crit :

I'm looking for the most idiomatic and elegant means of iterating over a
filtered subset of a collection. Here's the basic structure of piece of
code I'm looking at, which must be fairly common:

   Vector<Widget> widgets = doSomethingToGetWidgets();

   for (Widget widget : widgets) {
     if (widget instanceof ActionWidget) {
       doSomethingWithActionWidget( (ActionWidget) widget);
     }
   }

(obviously, ActionWidget is a subclass of Widget)

What I'd like to do would be something like

   Vector<Widget> widgets = doSomethingToGetWidgets();

   for (ActionWidget widget : widgets
    where (widget instanceof ActionWidget)) {
       doSomethingWithActionWidget( (ActionWidget) widget);
   }

I can't find anything in the Java 5 collections documentation which
offers type filtering functionality; am I missing something?


I personally find the code very easy to read and understand as is, but
you might be interested in apache commons collections :
http://commons.apache.org/collections/

The code could be rewritten as is :

List<Widget> widgets = doSomethingToGetWidgets();
CollectionUtils.forAllDo(widgets, ClosureUtils.ifClosure(
     PredicateUtils.instanceOfPredicate(ActionWidget.class),
     new Closure() {
         @Override
         public void execute(Object o) {
             doSomethingWithActionWidget((ActionWidget) o);
         }
     }));

(not compiled, not tested)

Please stop using Vector. List/ArrayList should be preferred.

JB.

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