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From: Eric Sosman <esosman@ieee-dot-org.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: for :each style question
Date: Wed, 30 Nov 2011 21:35:59 -0500
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On 11/30/2011 6:32 PM, Roedy Green wrote:
> In a for:each loop, sometimes you want to treat the first and or last
> element specially.
>
> The obvious way to handle is to revert to a for int i= loop and check
> for special values of i.
>
> You can keep the for:each style if you have a boolean first= true that
> you set false to detect the first.
>
> I don't know of an equivalent way to detect the last.
>
> In the olden days I would have handled the first and last cases
> outside the loop, with the loop running over the middle elements. You
> can't do that with for:each.
>
> What do you consider the best style to deal with this?

     I once taught a student whose DO loops (this was FORTRAN) always
iterated from 1 through N, never from 2 through N or 1 through N-1.
Paraphrasing into zero-based Java, he'd write something like

	for (int i = 0; i < array.length; ++i) {
	    if (i == 0) continue;
	    if (i == array.length - 1) continue;
	    massage(array[i-1], array[i], array[i+1]);
	}

     I was unable to break him of this habit, and eventually formed
the opinion that he had learned The One True Way to write a loop,
and Nothing On Earth would persuade him to write it differently.

     That's the wrong way to think about a tool.

     The for:each form is a convenience, a prepackaged solution to
a common problem.  Do not expect it to be the answer for all kinds
of iteration.  for:each is Java's feeble imitation of (mapc); don't
push it beyond its built-in limits.  There are lots of other looping
forms available; use them when they suit.

     (For those who don't know what (mapc) means, see the current
thread "java developers" and give special attention to Patricia
Shanahan's contribution.)

-- 
Eric Sosman
esosman@ieee-dot-org.invalid