Re: Enum Idiom Question

From:
"Rhino" <no.offline.contact.please@example.com>
Newsgroups:
comp.lang.java.programmer
Date:
Sat, 29 May 2010 16:43:23 -0400
Message-ID:
<htru9c$d1q$1@speranza.aioe.org>
"Jean-Baptiste Nizet" <jnizetNOSPAM@NOSPAMfree.fr> wrote in message
news:4c0121cc$0$17326$426a74cc@news.free.fr...

Rhino a ?crit :

I would seriously consider instead of the enum to have a boolean
plus a String, because true/false and a textual explanation is
really what you need.


Sorry, I meant to comment on this point too and didn't realize I had
missed it right away....

My little PadResult class started out with a boolean and a string with
the boolean indicating success or failure of the method and the string
containing either an error message or the padded version of the input
string. But when I looked at the invocation of PadResult and saw

  PadResult padResult = new PadResult(true, paddedString);

or

  PadResult padResult = new PadResult(false, errorMsg);

I found myself a bit challenged to remember if "true" meant "true, the
method produced a good result" or "true, the method found an error". I
could probably just memorize that true means a successful result or use
some boolean constants to make it clearer - see the example below - but I
thought it would be clearer still if I used a well-named enum value so I
went with the enum.


When a constructor's argument are not sufficiently clear, it might be a
good idea to use a factory method instead:

public class PadResult {

    private String result;
    private String errorMessage;
    private boolean successful;

    private PadResult(boolean successful, String resultOrErrorMessage) {
        this.successful = successful;
        if (successful) {
            this.result = resultOrErrorMessage;
        }
        else {
            this.errorMessage = resultOrErrorMessage;
        }
    }

    public static PadResult createSuccessfulResult(String result) {
        return new PadResult(true, result);
    }

    public static PadResult createFailedResult(String errorMessage) {
        return new PadResult(false, errorMessage);
    }

    // getters omitted
}

then your pad() method uses

    return PadResult.createSuccessfulResult(result);
or
    return PadResult.createFailedResult(errorMessage);

and it's much clearer.


I was starting to think along those lines myself before I saw your post but
was toying with a different approach: one constructor for a successful
result and a different constructor for a problem. I haven't actually tried
writing the code yet to see how much I liked it.

I appreciate your suggestion as another alternative. It looks like it should
work!

Thank you!

--
Rhino

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