OptimizedForLoopBenchmarks.java

package org.sample;

import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.logic.BlackHole;

import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.TimeUnit;

@Measurement(iterations = 5)
@Warmup(iterations = 5)
@Fork(3)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@State(Scope.Thread)
public class OptimizedForLoopBenchmarks {

  @Param({"1000", "10000", "100000", "1000000"})
  public int length;

  private List<Integer> list;
  private int[]         array;

  @Setup
  public void setup() {
    list = new LinkedList<>();
    array = new int[length];
    for(int c = 0; c < length; c++) {
      int i = 10000 + c;
      list.add(i);
      array[c] = i;
    }
  }

  @GenerateMicroBenchmark
  public void forLoopWithoutSideEffect() {
    for(Integer i : list) {}
  }

  @GenerateMicroBenchmark
  public void forLoopWithSideEffect(BlackHole bh) {
    for(Integer i : list) { bh.consume(i); }
  }

  @GenerateMicroBenchmark
  public void arrayForLoopWithoutSideEffect() {
    for(int i = 0; i < length; i++) {}
  }

  @GenerateMicroBenchmark
  public void arrayForLoopWithAssignment() {
    for(int i = 0; i < length; i++) {
      Object o = array[i];
    }
  }

  @GenerateMicroBenchmark
  public void arrayForLoopWithSideEffect(BlackHole bh) {
    for(int i = 0; i < length; i++) { bh.consume(array[i]); }
  }

}

Results

Mac OS X 10.8, JDK 1.7.0_21-b12

Benchmark                                                          (length)   Mode   Samples         Mean   Mean error    Units
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithAssignment       1000000   avgt         5  1128262.337    33368.956    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithAssignment        100000   avgt         5   112173.533     4046.902    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithAssignment         10000   avgt         5    13986.968       93.538    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithAssignment          1000   avgt         5     1403.978        1.508    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithSideEffect       1000000   avgt         5  1064127.764    28925.262    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithSideEffect        100000   avgt         5   103840.942     1244.817    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithSideEffect         10000   avgt         5    11209.971       86.001    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithSideEffect          1000   avgt         5     1140.299       17.599    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithoutSideEffect    1000000   avgt         5        0.335        0.481    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithoutSideEffect     100000   avgt         5        0.335        0.478    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithoutSideEffect      10000   avgt         5        0.337        0.484    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.arrayForLoopWithoutSideEffect       1000   avgt         5        0.335        0.478    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.forLoopWithSideEffect            1000000   avgt         5  5908654.747   146634.446    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.forLoopWithSideEffect             100000   avgt         5   320832.137    15636.930    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.forLoopWithSideEffect              10000   avgt         5    30878.899     2547.645    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.forLoopWithSideEffect               1000   avgt         5     3323.904      789.063    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.forLoopWithoutSideEffect         1000000   avgt         5  5327773.313   109109.714    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.forLoopWithoutSideEffect          100000   avgt         5   289448.064    23716.044    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.forLoopWithoutSideEffect           10000   avgt         5    27505.351     1082.344    ns/op
o.p.b.r.OptimizedForLoopBenchmarks.forLoopWithoutSideEffect            1000   avgt         5     2667.670       93.183    ns/op