new ArrayList vs. addAll

ArrayListCreate.java

import org.openjdk.jmh.annotations.*;

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

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@State(Scope.Thread)
public class ArrayListCreate {

    private List<Integer> orig;

    @Param({"100", "1000", "10000" })
    int size;

    @Setup
    public void setUp() {
        orig = new ArrayList<>();
        for (int i = 0; i < size; i++) {
            orig.add(i % 63);
        }
    }

    @Benchmark
    public ArrayList<Integer> addAll() {
        ArrayList<Integer> list = new ArrayList<>();
        list.addAll(orig);
        return list;
    }

    @Benchmark
    public ArrayList<Integer> newArrayList() {
        return new ArrayList<>(orig);
    }
}

/*
  Results:
  
  # JMH 1.17.5 (released 46 days ago)
  # VM version: JDK 1.8.0_121, VM 25.121-b13
  # VM invoker: C:\Program Files\Java\jdk1.8.0_121\jre\bin\java.exe
  # VM options: <none>
  # Warmup: 2 iterations, 2 s each
  # Measurement: 5 iterations, 3 s each
  # Timeout: 10 min per iteration
  # Threads: 4 threads, will synchronize iterations
  # Benchmark mode: Average time, time/op

  ...

  Benchmark                     (size)  Mode  Cnt   Score   Error  Units
  ArrayListCreate.addAll           100  avgt    5   0,413 ? 0,019  us/op
  ArrayListCreate.addAll          1000  avgt    5   3,220 ? 0,089  us/op
  ArrayListCreate.addAll         10000  avgt    5  31,063 ? 1,654  us/op
  ArrayListCreate.newArrayList     100  avgt    5   0,214 ? 0,004  us/op
  ArrayListCreate.newArrayList    1000  avgt    5   1,944 ? 0,038  us/op
  ArrayListCreate.newArrayList   10000  avgt    5  20,131 ? 1,961  us/op
*/