String.substring when beginIndex is the string's length

[Zoltan Sziladi]

Hi,

There are 2 things I do not understand about how substring works, hopefully
someone can shed some light on it.

1. When you call substring and you provide the string's length as
beginIndex, why does it return an empty string instead of throwing an
exception? You are effectively indexing outside of the string: you index a
character that is after the last character. Obviously this won't be changed
since probably lots of code depend on this already, but still, I just don't
get the logic behind it.

2. In this specific case (when beginIndex is the string's length) there
seem to be a lot of unnecessary method calls for returning an empty string:
    String constructor -> Arrays.copyOfRange -> System.arraycopy
All of these calls do some checks and in this case pass around 0's a lot,
even creating array of 0 length, etc.
My question is, would it make sense to include an if so that if subLen ==
0, then it would return an empty string? Or it has too much overhead if we
consider how often this case occurs and it would be better to lose on
performance on these rare occasions while keeping the general case 1 if
faster?

Thanks in advance!

Regards,
Zoltan