result.txt

# JMH version: 1.19
# VM version: JDK 1.8.0_101, VM 25.101-b13
# VM invoker: C:\Program Files\Java\jdk1.8.0_101\jre\bin\java.exe
# VM options: <none>

# Run complete. Total time: 00:18:42

Benchmark                  (collectionType)  (size)  Mode  Cnt    Score   Error  Units
ToArrayTest.normalToArray         ArrayList       0  avgt   30    3,731 ± 0,020  ns/op
ToArrayTest.normalToArray         ArrayList       1  avgt   30   12,402 ± 0,082  ns/op
ToArrayTest.normalToArray         ArrayList       5  avgt   30   15,737 ± 0,120  ns/op
ToArrayTest.normalToArray         ArrayList      10  avgt   30   21,685 ± 0,147  ns/op
ToArrayTest.normalToArray         ArrayList      20  avgt   30   35,245 ± 0,378  ns/op
ToArrayTest.normalToArray         ArrayList      30  avgt   30   49,381 ± 0,811  ns/op
ToArrayTest.normalToArray           HashSet       0  avgt   30    4,330 ± 0,025  ns/op
ToArrayTest.normalToArray           HashSet       1  avgt   30   31,083 ± 0,238  ns/op
ToArrayTest.normalToArray           HashSet       5  avgt   30   44,210 ± 0,288  ns/op
ToArrayTest.normalToArray           HashSet      10  avgt   30   62,428 ± 1,107  ns/op
ToArrayTest.normalToArray           HashSet      20  avgt   30   83,525 ± 1,206  ns/op
ToArrayTest.normalToArray           HashSet      30  avgt   30  126,942 ± 2,163  ns/op
ToArrayTest.normalToArray           TreeSet       0  avgt   30    4,734 ± 0,095  ns/op
ToArrayTest.normalToArray           TreeSet       1  avgt   30   26,284 ± 0,160  ns/op
ToArrayTest.normalToArray           TreeSet       5  avgt   30   39,548 ± 0,293  ns/op
ToArrayTest.normalToArray           TreeSet      10  avgt   30   57,699 ± 0,364  ns/op
ToArrayTest.normalToArray           TreeSet      20  avgt   30   97,943 ± 1,125  ns/op
ToArrayTest.normalToArray           TreeSet      30  avgt   30  133,310 ± 2,507  ns/op
ToArrayTest.oldToArray            ArrayList       0  avgt   30    3,429 ± 0,116  ns/op
ToArrayTest.oldToArray            ArrayList       1  avgt   30   25,638 ± 0,841  ns/op
ToArrayTest.oldToArray            ArrayList       5  avgt   30   32,813 ± 1,607  ns/op
ToArrayTest.oldToArray            ArrayList      10  avgt   30   39,479 ± 1,449  ns/op
ToArrayTest.oldToArray            ArrayList      20  avgt   30   47,414 ± 0,641  ns/op
ToArrayTest.oldToArray            ArrayList      30  avgt   30   60,191 ± 0,411  ns/op
ToArrayTest.oldToArray              HashSet       0  avgt   30    3,247 ± 0,080  ns/op
ToArrayTest.oldToArray              HashSet       1  avgt   30   31,977 ± 0,511  ns/op
ToArrayTest.oldToArray              HashSet       5  avgt   30   45,557 ± 0,515  ns/op
ToArrayTest.oldToArray              HashSet      10  avgt   30   59,399 ± 0,394  ns/op
ToArrayTest.oldToArray              HashSet      20  avgt   30   81,507 ± 0,808  ns/op
ToArrayTest.oldToArray              HashSet      30  avgt   30  123,301 ± 0,611  ns/op
ToArrayTest.oldToArray              TreeSet       0  avgt   30    3,638 ± 0,117  ns/op
ToArrayTest.oldToArray              TreeSet       1  avgt   30   24,148 ± 0,179  ns/op
ToArrayTest.oldToArray              TreeSet       5  avgt   30   41,170 ± 0,401  ns/op
ToArrayTest.oldToArray              TreeSet      10  avgt   30   59,199 ± 0,643  ns/op
ToArrayTest.oldToArray              TreeSet      20  avgt   30   96,660 ± 0,716  ns/op
ToArrayTest.oldToArray              TreeSet      30  avgt   30  131,524 ± 1,082  ns/op

ToArrayTest.java

package com.example;

import org.openjdk.jmh.annotations.*;

import java.util.*;
import java.util.concurrent.*;import java.util.function.Supplier;import java.util.stream.Collectors;import java.util.stream.IntStream;

@Fork(3)
@Warmup(iterations=10, time=500, timeUnit=TimeUnit.MILLISECONDS)
@Measurement(iterations=10, time=500, timeUnit=TimeUnit.MILLISECONDS)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.NANOSECONDS)
@State(Scope.Benchmark)
public class ToArrayTest {
  private static final int ARRAY_COPY_THRESHOLD = 20;
  public static final String[] EMPTY_STRING_ARRAY = new String[0];

  @Param({"0", "1", "5", "10", "20", "30"})
  private int size;

  @Param({"ArrayList", "HashSet", "TreeSet"})
  private String collectionType;

  private Collection<String> c;

  @Setup
  public void setup() throws Exception {
      Class<? extends Collection> aClass = Class.forName("java.util."+collectionType).asSubclass(Collection.class);
      Supplier<Collection<String>> supplier = () -> {
          try {
              //noinspection unchecked
              return aClass.newInstance();
          }
          catch (InstantiationException | IllegalAccessException e) {
              throw new RuntimeException(e);
          }
      };
      c = IntStream.range(0, size).mapToObj(String::valueOf).collect(Collectors.toCollection(supplier));
  }

  public static <T> T[] toArray(Collection<T> c, T[] sample) {
    final int size = c.size();
    if (size == sample.length && size < ARRAY_COPY_THRESHOLD) {
      int i = 0;
      for (T t : c) {
        sample[i++] = t;
      }
      return sample;
    }
    return c.toArray(sample);
  }

  public static String[] toStringArray(Collection<String> collection) {
    return collection == null || collection.isEmpty()
           ? EMPTY_STRING_ARRAY : toArray(collection, new String[collection.size()]);
  }

  @Benchmark
  public String[] oldToArray() {
      return toStringArray(c);
  }

  @Benchmark
  public String[] normalToArray() {
      return c.toArray(EMPTY_STRING_ARRAY);
  }
}