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Groups > comp.lang.java.programmer > #7798

Re: StringBuilder

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In article <4e655caa$0$308$14726298@news.sunsite.dk>, arne@vajhoej.dk 
says...
> > Whereby this code is slower:
> >
> > String res="";
> > for (int i=0; i<100; i++) {
> > res+=i+"*"+i+"="+(i*i)+"\n";
> > }
> > System.out.println(res);
> >
> > It is translated to the following code by the compiler, and
> > thus uses 100 new and 100 toString():
> >
> > String res="";
> > for (int i=0; i<100; i++) {
> > StringBuilder _buf=new StringBuilder(res);
> > _buf.append(i);
> > _buf("*");
> > _buf.append(i);
> > _buf.append("=");
> > _buf.append((i*i));
> > _buf.append("\n");
> > res=_buf.toString();
> > }
> > System.out.println(res);
> >
> > For more information see for example here:
> > http://caprazzi.net/posts/java-bytecode-string-concatenation-and-stringbuilder/
> 
> That has been known for 10-15 years.
> 
> It should be in any Java book above beginners level.

Like other ancient performance-practices that have been obsoleted by 
today's compilers?

We have been told that using StringBuffer was the better alternative.
Now compilers have switched from using StringBuffer for the above 
example to the unsynchronized StringBuilder. Those who have manually 
used the StringBuffer have stopped the compiler for doing that for them 
and must rely on the JITs lock elision algorithm.

So as long as this part of the code does not represent a critical 
performance-bottleneck, I would recommend to use the simple, stupid 
"slow" variant and hope for future compilers to detect and optimize that 
pattern.

> http://java.sun.com/developer/technicalArticles/Interviews/community/k
abutz_qa.html <

Kind regards,
Wanja



-- 
..Alesi's problem was that the back of the car was jumping up and down 
dangerously - and I can assure you from having been teammate to 
Jean Alesi and knowing what kind of cars that he can pull up with, 
when Jean Alesi says that a car is dangerous - it is. [Jonathan Palmer]

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---

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StringBuilder bob <bob@coolgroups.com> - 2011-09-04 19:45 -0700
  Re: StringBuilder Arne Vajhøj <arne@vajhoej.dk> - 2011-09-04 22:53 -0400
  Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-05 05:27 +0200
    Re: StringBuilder Arne Vajhøj <arne@vajhoej.dk> - 2011-09-05 19:34 -0400
      Re: StringBuilder Wanja Gayk <brixomatic@yahoo.com> - 2011-09-11 16:35 +0200
        Re: StringBuilder Arne Vajhøj <arne@vajhoej.dk> - 2011-09-11 16:48 -0400
          Re: StringBuilder Wanja Gayk <brixomatic@yahoo.com> - 2011-09-17 02:54 +0200
            Re: StringBuilder Roedy Green <see_website@mindprod.com.invalid> - 2011-09-17 00:27 -0700
            Re: StringBuilder Lew <lewbloch@gmail.com> - 2011-09-18 01:42 -0700
              Re: StringBuilder Wanja Gayk <brixomatic@yahoo.com> - 2011-09-19 00:59 +0200
                Re: StringBuilder Roedy Green <see_website@mindprod.com.invalid> - 2011-09-19 05:07 -0700
                Re: StringBuilder Jeff Higgins <jeff@invalid.invalid> - 2011-09-19 11:38 -0400
    Re: StringBuilder Roedy Green <see_website@mindprod.com.invalid> - 2011-09-05 17:01 -0700
    Re: StringBuilder Stanimir Stamenkov <s7an10@netscape.net> - 2011-09-17 19:56 +0300
      Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-17 20:35 +0200
      Re: StringBuilder Roedy Green <see_website@mindprod.com.invalid> - 2011-09-17 15:34 -0700
        Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-18 01:33 +0200
          Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-18 01:56 +0200
          Re: StringBuilder Roedy Green <see_website@mindprod.com.invalid> - 2011-09-17 20:58 -0700
        Re: StringBuilder Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-09-17 22:44 -0700
          Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-18 09:54 +0200
            Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-18 09:59 +0200
            Re: StringBuilder Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-09-18 07:28 -0700
          Re: StringBuilder Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-09-18 08:15 -0400
            Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-18 15:32 +0200
              Re: StringBuilder Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-09-18 09:50 -0400
                Re: StringBuilder Stanimir Stamenkov <s7an10@netscape.net> - 2011-09-18 17:08 +0300
                Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-18 22:13 +0200
                Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-18 22:29 +0200
                Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-18 22:39 +0200
          Re: StringBuilder Roedy Green <see_website@mindprod.com.invalid> - 2011-09-19 09:45 -0700
  Re: StringBuilder Roedy Green <see_website@mindprod.com.invalid> - 2011-09-05 11:08 -0700
    Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-05 23:54 +0200
      Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-06 00:06 +0200
      Re: StringBuilder Roedy Green <see_website@mindprod.com.invalid> - 2011-09-05 17:03 -0700
        Re: StringBuilder Jan Burse <janburse@fastmail.fm> - 2011-09-06 08:53 +0200

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