These are my results on my iMac using the parameters:
- Enter countMin,
countMax, countStep, stringMin, stringMax:
500 8001 500 50 100
- The += String operation is quite a bit longer than either StringBuilder.append or the explicit character array approach
- Interestingly, the StringBuilder and explicit character array approaches vary quite a bit, and they seem to converge after a while
- Only around 3,000 strings does the += operation become longer than 1/2 second, so I am perfectly happy using this approach of strings that are shorter than this.
Table data = output:
number
Plus
ns
Build
ns
Char ns
500
45,288,972
149,523
1,607,211
1000
59,902,915
146,094
1,983,651
1500
154,508,901
467,926
1,087,409
2000
313,943,292
493,729
1,042,908
2500
309,990,136
924,623
760,421
3000
435,333,748
358,273
265,833
3500
731,918,455
352,838
291,833
4000
472,027,412
415,499
330,397
4500
603,437,663
538,292
384,516
5000
741,941,303
526,332
439,440
5500
904,946,076
648,917
557,638
6000
1,087,404,315
704,373
525,105
6500
1,286,219,802
702,047
1,303,877
7000
1,507,183,980
815,784
631,819
7500
1,691,152,729
752,773
747,234
8000
1,946,127,465
924,957
795,926
Code:
// File: StringTests.java
// Date: Aug 30, 2018
// Author: Nicholas Duchon
// Purpose: some String tests
// > prepare random strings
// > compare String += vs StringBuilder
import java.util.Random;
import java.util.Scanner;
class StringTests {
static Random rn = new Random ();
public static void main (String [] args) {
int countMin, countMax, countStep, stringMin, stringMax;
System.out.print ("Enter countMin, countMax, countStep, stringMin, stringMax: ");
Scanner sc = new Scanner (System.in);
countMin = sc.nextInt ();
countMax = sc.nextInt ();
countStep = sc.nextInt ();
stringMin = sc.nextInt ();
stringMax = sc.nextInt ();
System.out.printf ("%10s %20s %20s %20s\n", "number", "Plus ns", "Build ns", "Char ns");
for (int cnt = countMin; cnt < countMax; cnt += countStep) {
String arr [] = lots (cnt, stringMin, stringMax);
long x = buildPlus (arr);
long y = buildBuild (arr);
long z = buildChar (arr);
System.out.printf ("%10d %,20d %,20d %,20d\n", cnt, x, y, z);
} // end tests
} // end main
static long buildPlus (String [] sa) {
long start, end;
start = System.nanoTime();
String st = "";
for (String s: sa) st += s;
end = System.nanoTime ();
return end - start;
} // end method buildPlus
static long buildBuild (String [] sa) {
long start, end;
start = System.nanoTime();
String st = "";
StringBuilder sb = new StringBuilder ();
for (String s: sa) sb.append (s);
end = System.nanoTime ();
st = sb.toString ();
return end - start;
} // end method buildBuild
static long buildChar (String [] sa) {
long start, end;
start = System.nanoTime();
int cnt = 0;
for (String s: sa) cnt += s.length();
char [] carr = new char [cnt];
for (int i =0, k = 0; i < sa.length; k += sa [i].length(), i++) {
char [] cs = sa[i].toCharArray();
for (int j = 0; j < sa[i].length(); j++)
carr [k] = cs [j];
}
String st = new String (carr);
end = System.nanoTime ();
return end - start;
} // end method buildChar
// creates lots of random strings
static String [] lots (int k, int min, int max) {
String [] sts = new String [k];
for (int i = 0; i < sts.length; i++)
sts [i] = rst (rn.nextInt (max - min) + min);
return sts;
} // end method lots
// create a random String of n characters
static String rst (int n) {
char [] ca = new char [n];
// use int +, THEN convert to char
// otherwise get a conversion error
for (int i = 0; i < n; i++)
ca[i] = (char)('a' + rn.nextInt (26));
String st = new String (ca);
return st;
} // end method rst
} // end class StringTests
Nick.