java.io.Writer uses CharSequence.toString()

[Bernd Eckenfels]

Hello,

yes I agree that has to be benchmarked. (And probably greatly varries
with the input length as well).


But besides the performance aspect I wanted to mention something else.
I had a password hashing API and wanted to switch from the typical
overwriteable char[] signature to a CharSequence. Because if the
password is only existing as a String there is no help in copying it to
a char[]. And depending on the source CharSequence can deal with all of
them. But then I noticed its quite hard to deal with CharSequences
where no intermediate Strings are constructed.

You asked about the "extract", I was inspired by Peters hint to
extractChar in StringUtil of OpenHFT. It is a scary magic in an
external API but it could be a internal shortcut within the JDK. I
would actally expect encoders to have the same shortcut for strings...

https://github.com/OpenHFT/Chronicle-Core/blob/master/src/main/java/net/openhft/chronicle/core/util/StringUtils.java

Gruss
Bernd


 Am Fri, 29 Jul 2016 18:21:37 +0100
schrieb Pavel Rappo <pavel.rappo at oracle.com>:

> Once again, while I agree in some places it could have been done a
> bit better probably, I would say it's good to a have a look at
> benchmarks first.
> 
> If they show there's indeed a big difference between
> 
>    char[] copy = new chars[charSequence.length()];
>    String s = charSequence.toString();
>    s.getChars(0, s.length, copy, 0);
> 
> and
> 
>    char[] copy = new chars[charSequence.length()];
>    charSequence.getChars(0, charSequence.length(), copy, 0);
> 
> it could justify an increase in complexity of CharBuffer.append or
> introducing a new default method (getChars/fillInto) into
> CharSequence. Possibly. Or maybe not. Because there might be some
> nontrivial effects we are completely unaware of.
> 
> Btw, what do you mean by "extract char[]" from StringBuilder? Do you
> want StringBuilder to give away a reference to its char[] outside? If
> not, than what's the difference between "extract char[]" from
> StringBuilder and "use String" in your algorithm?
> 
> The bottom line is whatever you suggest would likely need a good
> justification. To me it's not immediately obvious that something like
> this
> 
>     public CharBuffer append(CharSequence csq) {
>         if (csq == null) {
>             put("null");
>         } else if (csq instanceof StringBuilder) {
>             char[] chars = new char[csq.length()];
>             ((StringBuilder) csq).getChars(0, csq.length(), chars, 0);
>             put(chars);
>         } else if (csq instanceof StringBuffer) {
>             char[] chars = new char[csq.length()];
>             ((StringBuffer) csq).getChars(0, csq.length(), chars, 0);
>             put(chars);
>         } else if (csq instanceof CharBuffer) {
>             CharBuffer buffer = (CharBuffer) csq;
>             int p = buffer.position();
>             put(buffer);
>             buffer.position(p);
>         } else {
>             for (int i = 0; i < csq.length(); i++) {
>                 put(csq.charAt(i));
>             }
>         }
>         return this;
>     }
>     
> is better than this (what's there today)
> 
>     public CharBuffer append(CharSequence csq) {
>         if (csq == null)
>             return put("null");
>         else
>             return put(csq.toString());
>     }
> 
> > On 29 Jul 2016, at 15:12, ecki at zusammenkunft.net wrote:
> > 
> > Hello,
> > 
> > Have to agree with Fabian handling CharSequences (and special case
> > StringBuilder) is pretty weak, in CharBuffer.append(CharSequence)
> > you see the same toString. I would expect it to do:
> > - Instamceof String -> use it
> > - Instance of StringBuilder -> extract char[] and iterate
> > - Instance of CharBuffer -> handle
> > - Otherwise: Loop over charAt
> > 
> > (the otherwise might be a tradeof between allocation and
> > (not)inlined bounds checks) 
> > 
> > Alternative would be a CharSequence.fillInto(char[])
> > 
> > BTW wouldn't it be create if char[] implements CharSequence?
> > 
> > Gruss
> > Bernd
> > -- 
> > http://bernd.eckenfels.net
> > From Win 10 Mobile
> > 
> > Von: Fabian Lange
>