RFR: JDK-8197594: String#repeat

[Jim Laskey]

Roger,

Claes did some performance tests against an earlier implementation where I was doing just that. We determined that the performance difference was lost in the noise.

Cheers,

— Jim




> On Mar 1, 2018, at 10:11 AM, Roger Riggs <Roger.Riggs at oracle.com> wrote:
> 
> Hi Jim,
> 
> Perhaps premature optimization...
> 
> Have you done any JMH tests on the expected string content and sizes.  The optimization for single 8-bit characters
> is good but for short strings like inserting spaces for tab stops, "    ".repeat(5), will suffer the overhead of Arraycopy
> for very small/short or non-8-bit strings.   Perhaps use a regular loop below some threshold ( limit < 32).
> Maybe the intrinsic already handles this efficiently or it is not important enough to optimize.
> 
> I would not expect to see many very long repeats or long strings being repeated.
> And I would leave cache-effect optimizations to the implementation of Arraycopy.
> 
> Thanks, Roger
> 
> On 2/28/2018 9:13 PM, Paul Sandoz wrote:
>> Hi Jim,
>> 
>> Looks good. I like the power of 2 copying.
>> 
>> 
>> 2978      * @throws  IllegalArgumentException if the {@code count} is
>> 2979      *          negative.
>> 2980      */
>> 2981     public String repeat(int count) {
>> 
>> Missing @since11 on the method.
>> 
>> 
>> Like Stuart suggests, turn the explanatory text into an api note, perhaps with a small code sample.
>> 
>> Thanks,
>> Paul.
>>  
>>> On Feb 28, 2018, at 8:31 AM, Jim Laskey <james.laskey at oracle.com> wrote:
>>> 
>>> Introduction of a new instance method String::repeat to allow an efficient and concise approach for generating repeated character sequences as strings.
>>> 
>>> Performance information in JBS.
>>> 
>>> Thank you.
>>> 
>>> Cheers,
>>> 
>>> — Jim
>>> 
>>> 
>>> JBS: https://bugs.openjdk.java.net/browse/JDK-8197594 <https://bugs.openjdk.java.net/browse/JDK-8197594>
>>> CSR: https://bugs.openjdk.java.net/browse/JDK-8198296
>>> <http://cr.openjdk.java.net/~jlaskey/8197594/String.html>
>>> Webrev: http://cr.openjdk.java.net/~jlaskey/8197594/webrev-02/index.html <http://cr.openjdk.java.net/~jlaskey/8197594/webrev-02/index.html>
>>> JavaDoc: http://cr.openjdk.java.net/~jlaskey/8197594/String.html <http://cr.openjdk.java.net/~jlaskey/8197594/String.html>
>>> 
>>> 
>>> 
>