On Saturday, 1 March 2014 15:32:41 UTC+5:30, bob wrote:
>
> Case :
>
> clojure verison:
>
> (time (dotimes [n 10000000] (str n "another word"))) ;; take about 5000msec
>
> java version
>
> long time = System.nanoTime();
>
> for(int i=0 ; i<10000000 ;i++){
> String a=i+"another word";
> }
> System.out.println(System.nanoTime()-time);
>
>
> The java version take about 500 msecs, I thought it might be caused by the
> str implementation which is using string builder, and it might not be the
> best choice in the case of no much string to concat, and then I replace
> "another word" with 5 long strings as the parameter, however no surprise.
>
> I just wonder what make the difference, or how to find the difference.
>
Others have added useful points to this thread. Java string concatenation
internally uses StringBuilder, so if you replace (str n "another word")
with the following:
(let [sb (StringBuilder.)]
(.append sb n)
(.append sb "another word")
(.toString sb))
..then the perf improves 1/4 to 1/3. Further, with the following tweak:
(let [sb (StringBuilder. 20)] ; because StringBuilder allocates only 16
chars by default on Oracle JRE
(.append sb n)
(.append sb "another word")
(.toString sb))
..the perf improves from 1/3 to less than 1/2. Here we simply avoid double
allocation in StringBuilder.
Other things I made sure were:
1. I used Criterium to measure
2. I used `-server` option
3. Made sure reflection warning was on
Shantanu
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