java - getDeclaredFields() absolute performance -

i have java class represents entry in database. each field column in database.

when want update database, construct contentvalues object.

is

arraylist<t> contentvalues = new arraylist<t>()  //bla bla add ten items contentvalues` 

faster than

arraylist<t> = new arraylist<t>(thisclass.class.getdeclaredfields().length); //bla bla add ten items contentvalues 

what absolute performance of getdeclaredfields? hope point out how getdeclaredfields works. know how resize of container works don't know how getdeclaredfields works , how perform.

micro benchmark simple hashmap using same settings contentvalues (assuming class referring to), , adding 10 fields (i.e. 1 resizing operation):

benchmark                                    mean   mean error          var    units c.a.p.g.a.reflection.getdeclaredfields     326.405        5.989       33.961  nsec/op c.a.p.g.a.reflection.resize                247.581        7.377       51.520  nsec/op 

so getdeclaredfields slower resizing map once, difference of order of 100 nanoseconds on desktop pc.

when adding more fields thisclass, getdeclaredfields gets slower, favour auto-resizing approach.

code:

@generatemicrobenchmark(benchmarktype.averagetimeperop) public map getdeclaredfields() {     map m = new hashmap(thisclass.class.getdeclaredfields().length, 1.0f);     (int = 0; < 9; i++) {         m.put(i, "a");     }     return m; }  @generatemicrobenchmark(benchmarktype.averagetimeperop) public map resize() {     map m = new hashmap(8, 0.75f);     (int = 0; < 9; i++) {         m.put(i, "a");     }     return m; }  class thisclass {     private int i, j, k;     public string s, t, u;     protected list l, m, n; }