PrimCollector.java

import java.util.concurrent.TimeUnit;
import javax.util.streamex.*;
import java.util.stream.*;
import java.util.*;

import org.openjdk.jmh.infra.Blackhole;
import org.openjdk.jmh.annotations.*;

@Warmup(iterations = 5, time = 1000, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 1000, timeUnit = TimeUnit.MILLISECONDS)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@Fork(2)
@State(Scope.Benchmark)
public class PrimCollector {
    @Param({ "100", "10000", "1000000" })
    private int n;

    private int[] input;

    @Setup
    public void setUp() {
        input = new Random(1).ints(n, -1000, 1000).toArray();
    }

    @Benchmark
    public void sumBySign(Blackhole bh) {
        Map<Boolean, Integer> sums = IntStreamEx.of(input)
             .collect(IntCollector.partitioningBy(i -> i > 0, IntCollector.summing()));
        bh.consume(sums);
    }

    @Benchmark
    public void sumBySignBoxed(Blackhole bh) {
        Map<Boolean, Integer> sums = IntStream.of(input).boxed()
             .collect(Collectors.partitioningBy(i -> i > 0, Collectors.summingInt(Integer::intValue)));
        bh.consume(sums);
    }

    @Benchmark
    public void joining(Blackhole bh) {
        String nums = IntStreamEx.of(input).collect(IntCollector.joining(","));
        bh.consume(nums);
    }

    @Benchmark
    public void joiningBoxed(Blackhole bh) {
        String nums = IntStream.of(input).mapToObj(String::valueOf)
          .collect(Collectors.joining(","));
        bh.consume(nums);
    }


    @Benchmark
    public void groupByLastDigit(Blackhole bh) {
        Map<Integer, int[]> groups = IntStreamEx.of(input)
          .collect(IntCollector.groupingBy(i -> i % 10));
        bh.consume(groups);
    }

    @Benchmark
    public void groupByLastDigitBoxed(Blackhole bh) {
        Map<Integer, List<Integer>> groups = IntStream.of(input).boxed()
          .collect(Collectors.groupingBy(i -> i % 10));
        bh.consume(groups);
    }
}

results.txt

Benchmark                                (n)  Mode  Cnt      Score      Error  Units
PrimCollector.groupByLastDigit           100  avgt   20      2.676 ±    0.008  us/op
PrimCollector.groupByLastDigit         10000  avgt   20    217.997 ±    2.978  us/op
PrimCollector.groupByLastDigit       1000000  avgt   20  22062.558 ±   71.004  us/op
PrimCollector.groupByLastDigitBoxed      100  avgt   20      2.503 ±    0.098  us/op
PrimCollector.groupByLastDigitBoxed    10000  avgt   20    277.244 ±    1.345  us/op
PrimCollector.groupByLastDigitBoxed  1000000  avgt   20  28364.470 ±  356.520  us/op
PrimCollector.joining                    100  avgt   20      2.993 ±    0.013  us/op
PrimCollector.joining                  10000  avgt   20    326.926 ±    3.930  us/op
PrimCollector.joining                1000000  avgt   20  33277.548 ± 1013.316  us/op
PrimCollector.joiningBoxed               100  avgt   20      5.053 ±    0.020  us/op
PrimCollector.joiningBoxed             10000  avgt   20    580.392 ±    2.971  us/op
PrimCollector.joiningBoxed           1000000  avgt   20  63284.896 ±  828.737  us/op
PrimCollector.sumBySign                  100  avgt   20      0.192 ±    0.001  us/op
PrimCollector.sumBySign                10000  avgt   20     13.161 ±    0.016  us/op
PrimCollector.sumBySign              1000000  avgt   20   1411.781 ±   71.582  us/op
PrimCollector.sumBySignBoxed             100  avgt   20      0.775 ±    0.002  us/op
PrimCollector.sumBySignBoxed           10000  avgt   20     72.342 ±    0.306  us/op
PrimCollector.sumBySignBoxed         1000000  avgt   20   8005.887 ±   32.117  us/op