java - Pattern.split slower than String.split -

there 2 methods:

private static void normalsplit(string base){     base.split("\\."); }  private static final pattern p = pattern.compile("\\.");  private static void patternsplit(string base){     //use static field above     p.split(base);  } 

and test them in main method:

public static void main(string[] args) throws exception{     long start = system.currenttimemillis();     string longstr = "a.b.c.d.e.f.g.h.i.j";//use long string     for(int i=0;i<300000;i++){         normalsplit(longstr);//switch patternsplit see difference     }     system.out.println((system.currenttimemillis()-start)/1000.0); } 

intuitively,i think string.split call pattern.compile.split (after lot of work) real thing. can construct pattern object in advance (it thread safe) , speed splitting.

but fact is, using pre-constructed pattern much slower calling string.split directly. tried 50-character-long string on them (using myeclipse), direct call consumes half time of using pre-constructed pattern object.

please can tell me why happens ?

this may depend on actual implementation of java. i'm using openjdk 7, , here, string.split indeed invoke pattern.compile(regex).split(this, limit), only if string split by, regex, more single character.

see here source code, line 2312.

public string[] split(string regex, int limit) {    /* fastpath if regex       (1)one-char string , character not 1 of          regex's meta characters ".$|()[{^?*+\\", or       (2)two-char string , first char backslash ,          second not ascii digit or ascii letter.    */    char ch = 0;    if (((regex.count == 1 &&        // bunch of other checks , lots of low-level code        return list.sublist(0, resultsize).toarray(result);    }    return pattern.compile(regex).split(this, limit); } 

as splitting "\\.", using "fast path". is, if using openjdk.