8069325: Pattern.splitAsStream does not return input if it is empty and there is no match

[Paul Sandoz]

On Jan 20, 2015, at 5:35 PM, Xueming Shen <xueming.shen at oracle.com> wrote:

> On 1/20/15 8:17 AM, Paul Sandoz wrote:
>> Hi,
>> 
>> http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8069325-Pattern-splitAsStream-emptyInput/webrev/
>> 
>> This patch fixes an edge case in Pattern.splitAsStream for matching against an empty input string, which deviated from the behaviour of Pattern.split. When there are no matches a stream containing the input string should be returned rather than an empty stream.
>> 
>> --
>> 
>> I have kept compatibility with Pattern.split(String ) but i noticed another an edge case.
>> 
>> What should the following return:
>> 
>>   Pattern.compile("").split("")
>> 
>> [] or [""]?
>> 
>> There is a zero-width match at the beginning and an empty remaining segment both of which should be discarded, as such i would expect the result to be [] rather than as [""], as currently produced result.
> 
> It may depend on how the "trailing empty string"  gets interpreted. Is it possible to interpret it as the
> empty string is the result of the "substring from the beginning 0-width match and the end of the input
> sequence", any thing after that is "trailing"?
> 

Seems a stretch to me. Consider the following which returns []:

  Pattern.compile("x").split("x");

Replace "x" with "" and intuitively i would expect the same behaviour.


> It would be clear if the spec explicitly said, the result of splitting an empty input is an empty string.
> 
> I would assume someone, mostly the user of String.split(), will get hit by this "incompatible" change.
> 

Yeah, there is some risk in that.

Paul.