Henri Yandell wrote at Freitag, 5. März 2010 10:32:
> 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.
> 2) subSequence returns CharSequence and not T.
Because you do not necessarily get the same type. The API gives room for
optimized types.
> 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?
Since the most important implementations (String/StringBuilder/StringBuffer)
all return effectively a String, you may actually return one also:
public static String left(CharSequence str, int len) {
if (str == null) {
return null;
}
return str.subSequence(0, len).toString();
}
Opinions?
- Jörg
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