RFR: 8197594 - String and character repeat

[forax at univ-mlv.fr]

----- Mail original -----
> De: "Jim Laskey" <james.laskey at oracle.com>
> À: "Remi Forax" <forax at univ-mlv.fr>
> Cc: "Brian Goetz" <brian.goetz at oracle.com>, "core-libs-dev" <core-libs-dev at openjdk.java.net>
> Envoyé: Jeudi 15 Février 2018 21:16:48
> Objet: Re: RFR: 8197594 - String and character repeat

>> On Feb 15, 2018, at 4:04 PM, Remi Forax <forax at univ-mlv.fr> wrote:
>> 
>> I'm not sure we need 4, it's just a convenient method that may be slower than if
>> the user code calls toString() (because of profile pollution),
>> so i'm not sure i pull it's own weight.
>> 
>> And about adding a default method into CharSequence, the default method should
>> return a CharSequence or String ?
> 
> If you mean each class returns an instance of its class, I think that overlaps
> Appendable..

yes, very true

> 
>> and what about the other implementations, AbstractStringBuilder and CharBuffer
>> at least ?
> 
> This falls into the Appendable.append( T t, int count) realm mentioned
> originally.
> 
> Long term this could be a goal, and maybe defaulting CharSequence#repeat
> returning a string would be shortsighted.
> 
> But, I think having instance String#repeat returning a CharSequence would limit
> its use (methods expecting strings.)

yes, i think we should play safe here and only add repeat to String.

> 
> — Jim

Rémi

> 
>> 
>> Rémi
>> 
>> ----- Mail original -----
>>> De: "Jim Laskey" <james.laskey at oracle.com>
>>> À: "Brian Goetz" <brian.goetz at oracle.com>
>>> Cc: "core-libs-dev" <core-libs-dev at openjdk.java.net>
>>> Envoyé: Jeudi 15 Février 2018 18:34:19
>>> Objet: Re: RFR: 8197594 - String and character repeat
>> 
>>> Very reasonable approach.
>>> 
>>> 
>>>> On Feb 15, 2018, at 1:31 PM, Brian Goetz <brian.goetz at oracle.com> wrote:
>>>> 
>>>> I suggest merging 1 and 4 by making it an instance method on CS with a default
>>>> in CS and an override on string and string builder?
>>>> 
>>>> Sent from my MacBook Wheel
>>>> 
>>>>> On Feb 15, 2018, at 9:20 AM, Jim Laskey <james.laskey at oracle.com> wrote:
>>>>> 
>>>>> This is a pre-CSR code review [1] for String repeat methods (Enhancement).
>>>>> 
>>>>> The proposal is to introduce four new methods;
>>>>> 
>>>>> 1. public String repeat(final int count)
>>>>> 2. public static String repeat(final char ch, final int count)
>>>>> 3. public static String repeat(final int codepoint, final int count)
>>>>> 4. public static String repeat(final CharSequence seq, final int count)
>>>>> 
>>>>> For the sake of transparency, only 1 is necessary, 2-4 are convenience methods.
>>>>> In the case of 2, “*”.repeat(10) performs as well as String.repeat(‘*’, 10).
>>>>> 3 and 4 convert to String before calling 1.
>>>>> 
>>>>> Performance runs with jmh (results as comment in [2]) show that these
>>>>> methods are significantly faster that StringBuilder equivalents.
>>>>> - fewer memory allocations
>>>>> - fewer char to byte array conversions
>>>>> - faster pyramid replication vs O(N) copying
>>>>> 
>>>>> I left StringBuilder out of scope. It falls under the category of
>>>>> Appendables#append with repeat. A much bigger project.
>>>>> 
>>>>> All comments welcome. Especially around the need for convenience
>>>>> methods, the JavaDoc content and expanding the tests.
>>>>> 
>>>>> — Jim
>>>>> 
>>>>> [1] webrev: http://cr.openjdk.java.net//oj/home/jlaskey/8197594/webrev-00
>>>>> [2] jbs: https://bugs.openjdk.java.net/browse/JDK-8197594