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  1. import java.util.Random;
  2. import java.lang.System;
  3.  
  4. class ShuffleTest {
  5.     private static abstract class Generator {
  6.         public abstract String generate();
  7.     }
  8.  
  9.     private static final class GeneratorRolfl extends Generator {
  10.         private final Random rand = new Random();
  11.         private final char[] digits = "0123456789".toCharArray();
  12.  
  13.         public final String generate() {
  14.             int index = digits.length;
  15.             // Fisher-Yates.
  16.             while (index > 1) {
  17.                 final int pos = rand.nextInt(index--);
  18.                 final char tmp = digits[pos];
  19.                 digits[pos] = digits[index];
  20.                 digits[index] = tmp;
  21.             }
  22.             return new String(digits);
  23.         }
  24.     }
  25.  
  26.     private static final class GeneratorIlmari extends Generator {
  27.         private final Random rand = new Random();
  28.         private final char[] digits = new char[10];
  29.  
  30.         public final String generate() {
  31.             digits[0] = '0';
  32.             for (int index = 1; index < digits.length; index++) {
  33.                 final int pos = rand.nextInt(index + 1);
  34.                 digits[index] = digits[pos];
  35.                 digits[pos] = (char) ('0' + index);
  36.             }
  37.             return new String(digits);
  38.         }
  39.     }
  40.  
  41.     public static void main (String args[]) {
  42.         Generator generators[] = { new GeneratorRolfl(), new GeneratorIlmari() };
  43.         int iterations = 1000000, burnin = 10000;
  44.  
  45.         if (args.length > 0) {
  46.             iterations = Integer.parseInt( args[0] );
  47.         }
  48.         if (args.length > 1) {
  49.             burnin = Integer.parseInt( args[1] );
  50.         }
  51.  
  52.         for (Generator gen: generators) {
  53.             System.out.println("Burning in " + gen.getClass().getName() + " for " + burnin + " iterations...");
  54.             for (int i = 0; i < burnin; i++) {
  55.                 gen.generate();
  56.             }
  57.             System.out.println("Benchmarking " + gen.getClass().getName() + " for " + iterations + " iterations...");
  58.             long t0 = System.nanoTime();
  59.             for (int i = 0; i < iterations; i++) {
  60.                 gen.generate();
  61.             }
  62.             long t1 = System.nanoTime();
  63.             System.out.println("Elapsed time: " + (t1 - t0) * 1.0e-9 + " seconds");
  64.         }
  65.     }
  66. }
Success #stdin #stdout 1.2s 380480KB
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Burning in ShuffleTest$GeneratorRolfl for 10000 iterations...
Benchmarking ShuffleTest$GeneratorRolfl for 1000000 iterations...
Elapsed time: 0.56381232 seconds
Burning in ShuffleTest$GeneratorIlmari for 10000 iterations...
Benchmarking ShuffleTest$GeneratorIlmari for 1000000 iterations...
Elapsed time: 0.543000004 seconds
https://ideone.com/J1dnGO
language:
Java (HotSpot 12)
created:
10 years ago
visibility:
public

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