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Subject: Re: "less for more" - a little story about String.split
Date: Sat, 28 Jul 2018 01:16:46 GMT
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On Fri, 27 Jul 2018 06:33:17 -0000 (UTC), Andreas Leitgeb
<avl@logic.at> wrote:

>Imagine you have a variable named "text" of type String, and then you
>have this line of code:
>   String lines[] = text.split( "\n" );
>
>If text originally pointed to an empty string, then you get an array
>of length 1, holding an empty string.
>
>If, however, you append a certain char to that string, then you may
>end up with a zero-length array returned from split!  Namely, if ...
>(***  drum roll ***)
>...the char you added matches split's delimiter: text.equals("\n").
>
>The javadoc of String.split gives these clues about array length in
>the case of a 0 limit:
>
>We have clue #1a:
>" The array returned by this method contains each substring of this
>" string that is terminated by another substring that matches the given
>" expression *or is terminated by the end of the string*. [my emphasis]
>[this essentially describes the effect of split with a negative limit]
>
>We have clue #1b:
>" If the expression does not match any part of the input then the
>" resulting array has just one element, namely this string.
>[This is just a corollary of #1a for the case of no matches.]
>
>and we have clue #2:
>" If n is zero then the pattern will be applied as many times as
>" possible, the array can have any length,
>" *and trailing empty strings will be discarded*. [again my emphasis]
>
>Which overrides #1a but not #1b.
>
>Could anyone explain to me, why emphasiszed part of clue #2 only
>applies to a String that contains at least one delimiter?  Why is
>clue #2 weaker than clue #1b but stronger than clue #1a ?
>
>Who else ever had a bug from wrongly assuming that split would
>always return an array of length at least 1, or maybe the other
>way: expecting 0-length arrays for splitting the empty string
>with a limit 0?

A cursory reading of the spec suggests that split can indeed return
zero strings when limit=0. "...and trailing empty strings will be
discarded", it says it right there. If the result contains nothing
*but* empty strings, why would you expect any different?

It looks like you get to keep all substrings, even empty ones, by
setting limit!=0.

The implied exception seems to be that the above does not apply to a
string that contains no matching delimiters, which is simply returned
as-is, even if it's empty.

But I'm new to Java, maybe I'm reading the spec wrong.