When I replaced the current implementation of StringUtils.left(String,int) with:
@SuppressWarnings("unchecked")
public static <T extends CharSequence> T left(T cs, int len) {
if (cs == null) {
return null;
}
if (len < 0) {
return (T) cs.subSequence(0, 0);
}
if (cs.length() <= len) {
return cs;
}
return (T) cs.subSequence(0, len);
}
Everything compiled, all tests passed, and no Unnecessary cast warnings came up
(as provided by Eclipse 3.6M5)
The problem is what happens when you pass in a non-Strings, like a
StringBuilder. The implementation of subsequence for StringBuilder returns a
new String, not new StringBuilder.
So it looks like StringUtils APIs need to be considered one at a time, and
tested with more than one CharSequence implementation (String, StringBuilder,
StringBuffer at least)
Gary Gregory
Senior Software Engineer
Seagull Software
email: [email protected]
email: [email protected]
www.seagullsoftware.com
> -----Original Message-----
> From: Niall Pemberton [mailto:[email protected]]
> Sent: Friday, March 05, 2010 02:41
> To: Commons Developers List
> Subject: Re: [lang] LANG-510
>
> On Fri, Mar 5, 2010 at 9:32 AM, Henri Yandell <[email protected]> wrote:
> > Thinking further on moving StringUtils to CharSequence, I'd like to
> > take the String left(String, int) method as an example. It depends on
> > substring(int, int), so is entirely possibly to move over to
> > subSequence(int, int).
> >
> > Hypothetical new method:
> >
> > CharSequence left(CharSequence, int)
> >
> > The downside here is that users currently storing this in a String are
> > going to have to cast. Generics to the rescue.
> >
> > <T extends CharSequence> T left(T, int)
> >
> > This hits two problems:
> >
> > 1) EMPTY is returned when the int is less than 0; EMPTY is a String and not
> T.
>
> From CharSequence's subSequence() javadoc "if start == end then an
> empty sequence is returned". So you could do:
>
> return (T)str.subSequence(0, 0);
>
> Niall
>
>
> > 2) subSequence returns CharSequence and not T.
> >
> > I could add a wrapper method to make Strings nicer:
> >
> > public static String left(String str, int len) {
> > if (str == null) {
> > return null;
> > }
> > return left( (CharSequence) str, len).toString();
> > }
> >
> > But that doesn't help the StringBuffer/StrBuilder/StringBuilder user;
> > they still get a sucky API.
> >
> > Am I missing anything obvious here, or should I give up the ghost on
> > trying to take these methods to CharSequence APIs?
> >
> > Hen
>
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