Hi,
Copy/paste is almost always brings more of a liability than an asset
due to long term maintenance, skew, etc.
Another possibility for StringJoiner is to look at the approach being
investigated
for String.format in JEP 348[1].
It leverages the work already done to support String concatenation ("+")
in JEP 280[2].
[1] https://openjdk.java.net/jeps/348
[2] https://openjdk.java.net/jeps/280
Regards, Roger
On 3/8/19 8:00 PM, Ivan Gerasimov wrote:
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
