RFR: 8197594 - String and character repeat

Roger Riggs Roger.Riggs at Oracle.com
Thu Feb 15 20:38:02 UTC 2018

Hi Jim,

Its cleaner to do the API (CSR) review before and without the 
It helps keep the issues separate.

Don't make statements about count == Integer.MAX_VALUE / 2.
There is no point, unless it should throw IAE.

On 2/15/2018 3:16 PM, Jim Laskey wrote:
>> 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..
Beware thinking about default methods on interfaces; the dragons will 
get you.
Recently, this was discussed in the context of Reader.transferTo.
>> 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.)
There is no point in returning CharSequence, a String is a CharSequence 
and can be used anywhere
a CharSequence can.

$.02, Roger

> — Jim
>> 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

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