java - string split performance down after one code -
i test sting.split below.
import java.io.file; public class testsplit3 { private static final string procfs = "/proc/"; public static void main(string[] args) { //split(); testfile(integer.parseint(args[0]) > 0); split(); } private static void testfile(boolean flag) { long start = system.currenttimemillis(); if (flag) { (int = 0; < 1000; i++) { new file(procfs + i); } } system.out.println("newfile:" + (system.currenttimemillis() - start)); } public static void split() { long start = system.currenttimemillis(); (int j = 0; j < 1000; j++) { (int = 0; < 1000; i++) { string str = "asas asa s asas asas asa sa sas as a" + "asa sasa sa sa sas as asas as as as" + "as sas asdasdas dasd asda sd ada d"; str.tostring().split(" "); } } system.out.println("split:" + (system.currenttimemillis() - start)); } } , test result: [mapred@r03c02038 longer]$ ~/opt/taobao/install/jdk-1.7.0_10/bin/java testsplit3 0 newfile:0 split:1772 [mapred@r03c02038 longer]$ ~/opt/taobao/install/jdk-1.7.0_10/bin/java testsplit3 1 newfile:6 split:1763 [mapred@r03c02038 longer]$ ~/jdk-1.6.0_32/bin/java testsplit3 0 newfile:0 split:2833 [mapred@r03c02038 longer]$ [mapred@r03c02038 longer]$ ~/jdk-1.6.0_32/bin/java testsplit3 1 newfile:5 split:3416
e,in jdk7, running time consistent .but in jdk6 , 'testsplit3 0' faster 'testsplit3 1'. can tell me why??and how improve in jdk6
it due fact benchmark flawed.
a benchmark in java needs take account of fact of "jvm warmup" effects occur when start executing program:
- code may loaded "on demand".
- classes initialized "on demand".
- methods jit compiled after executing executing bit.
- by default heap starts "small" , may grows ... after each gc cycle.
these effects mean initial results benchmark loop may anomalous. code takes 1 measurement, , there's no way tell whether "warmup" effect distorting it.
reference:
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