Wonder if you should not move the test into StringLatin1.newString and
StringUTF16.newString to return "" if subLen [len] == 0. Then there would be an
across the board benefit.
> On Feb 25, 2020, at 11:43 AM, Сергей Цыпанов <sergei.tsypa...@yandex.ru>
> wrote:
>
> Hello,
>
> current implementation of String.substring(int,int) has a fast-path for the
> case when beginIndex = 0 and endIndex = length.
>
> I think there should be similar fast-path for the case beginIndex = endIndex
> (asuming both are valid):
>
> diff --git a/src/java.base/share/classes/java/lang/String.java
> b/src/java.base/share/classes/java/lang/String.java
> --- a/src/java.base/share/classes/java/lang/String.java
> +++ b/src/java.base/share/classes/java/lang/String.java
> @@ -1900,10 +1900,13 @@
> public String substring(int beginIndex, int endIndex) {
> int length = length();
> checkBoundsBeginEnd(beginIndex, endIndex, length);
> - int subLen = endIndex - beginIndex;
> if (beginIndex == 0 && endIndex == length) {
> return this;
> }
> + int subLen = endIndex - beginIndex;
> + if (subLen == 0) {
> + return "";
> + }
> return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
> : StringUTF16.newString(value, beginIndex, subLen);
> }
>
> With this call to str.substring(n,n) will be allocation-free.
>
> Regards,
> Sergey Tsypanov
