Benchmarking of toArray

ToArrayBench.java

@State(Scope.Benchmark)
public class ToArrayBench {

    ArrayList<Byte> list;

    @Setup
    public void setup() throws Throwable
    {
        list = new ArrayList<>();
        for (int i = 0; i < 10; i++) {
            list.add((byte) i);
        }
    }

    @Benchmark
    public void zero_sized_array()
    {
        list.toArray(new Byte[0]);
    }

    @Benchmark
    public void simple_toArray()
    {
        list.toArray();
    }

    @Benchmark
    public void sized_array_from_list()
    {
        list.toArray(new Byte[list.size()]);
    }

    @Benchmark
    public void sized_array_fixed_size()
    {
        list.toArray(new Byte[100]);
    }

    @Benchmark
    public void defensive_copy()
    {
        new ArrayList<>(list);
    }

    public static void main(String[] args) throws RunnerException, IOException
    {
        Options opt = new OptionsBuilder().include(".*" + ToArrayBench.class.getSimpleName() + ".*")
                .warmupIterations(20)
                .warmupTime(TimeValue.seconds(1))
                .measurementIterations(20)
                .timeUnit(TimeUnit.MILLISECONDS)
                .forks(1)
                // .addProfiler(LinuxPerfProfiler.class)
                .build();

        new Runner(opt).run();
    }
}

Routinely, I will chew on people who can't use perfasm profiler, but this is not your fault it wasn't helping here. ;) Only in JMH 1.5+ (released yesterday) perfasm can decode the VM stubs, and VM stubs are the crucial piece of info to untangle this. See: http://cr.openjdk.java.net/~shade/scratch/ToArrayBench.java