[PATCH] enhancement proposal for String concatenation

[Ivan Gerasimov]

Hi Sergei!

As you said, this new class is pretty much like StringJoiner with 
reduced functionality.

For appending all elements of an Iterable you could use list.forEach(s 
-> sj.add(s)).

With kind regards,
Ivan

On 3/8/19 11:22 AM, Сергей Цыпанов wrote:
> Hello,
>
> I have an enhancement proposal for some cases of String concatenation in Java.
>
> Currently we concat Strings mostly using java.lang.StringBuilder. The main disadvantage of StringBuilder is underlying char array or rather a need to resize it when the capacity is about to exceed array length and subsequent copying of array content into newly allocated array.
>
> One alternative solution existing is StringJoiner. Before JDK 9 it was a kind of decorator over StringBuilder, but later it was reworked in order to store appended Strings into String[] and overall capacity accumulated into int field. This makes it possible to allocate char[] only once and of exact size in toString() method reducing allocation cost.
>
> My proposal is to copy-paste the code of StringJoinder into newly created class java.util.StringChain, drop the code responsible for delimiter, prefix and suffix and use it instead of StringBuilder in common StringBuilder::append concatenation pattern.
>
> Possible use-cases for proposed code are:
> - plain String concatenation
> - String::chain (new methods)
> - Stream.collect(Collectors.joining())
> - StringConcatFactory
>
> We can create new methods String.chain(Iterable<CharSequence>) and String.chain(CharSequence...) which allow to encapsulate boilerplate code like
>
>
>    StringBuilder sb = new StringBuilder();
>    for (CharSequence cs : charSequences) {
>      sb.append(cs);
>    }
>    String result = sb.toString():
>
>
> into one line:
>
>
>    String result = String.chain(charSequences);
>
>
>
> As of performance I've done some measurements using JMH on my work machine (Intel i7-7700) for both Latin and non-Latin Strings of different size and count.
> Here are the results:
>
> https://github.com/stsypanov/string-chain/blob/master/results/StringBuilderVsStringChainBenchmark.txt
>
> There is a few corner cases (e.g. 1000 Strings of length 1 appended) when StringBuilder takes over StringChain constructed with default capacity of 8, but StringChain constructed with exact added Strings count almost always wins, especially when dealing with non-Latin chars (Russian in my case).
>
> I've also created a separate repo on GitHub with benchmarks:
>
> https://github.com/stsypanov/string-chain
>
> Key feature here is ability to allocate String array of exact size is cases we know added elements count.
> Thus I think that if the change will be accepted we can add also an overloaded method String.chain(Collection<CharSequence>) as Collection::size allows to contruct StringChain of exact size.
>
> Patch is attached.
>
> Kind regards,
> Sergei Tsypanov

-- 
With kind regards,
Ivan Gerasimov