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
