For http://stackoverflow.com/q/36988704/4856258

SumNegSubarrays.java

import java.util.concurrent.*;
import java.util.stream.*;
import java.util.function.*;
import java.util.*;
import one.util.streamex.*;

import org.openjdk.jmh.infra.Blackhole;
import org.openjdk.jmh.annotations.*;
 
@Warmup(iterations = 5, time = 500, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@Fork(3)
@State(Scope.Benchmark)
public class SumNegSubarrays {
   @Param({"20", "200", "2000"})
   int n;

   int[] a;

   @Setup(Level.Iteration)
   public void setup() {
      a = new int[n];
      for (int i = 0; i < n; i ++)
          a[i] = ThreadLocalRandom.current().nextInt(-20, 21);
   }

   @Benchmark
   public long plain() {
        long global = 0;
        for (int i = 0; i < a.length; i++) {
            long sum = 0, negs = 0;
            for (int j = i; j < a.length; j++) {
                sum += a[j];
                if (sum < 0)
                    negs += 1;
            }
            global += negs;
        }
        return global;
   }

   @Benchmark
   public long stream() {
    return IntStream.range(0, a.length)
            .flatMap(from -> IntStream.rangeClosed(from + 1, a.length)
                    .map(to -> Arrays.stream(a, from, to).sum()))
            .filter(sum -> sum < 0)
            .count();
   }

   @Benchmark
   public long streamEx() {
	return IntStreamEx.range(a.length)
			.mapToObj(from -> IntStreamEx.of(a, from, a.length).scanLeft(Integer::sum))
			.flatMapToInt(IntStreamEx::of)
			.less(0)
			.count();
   }
}