Performance of variable argument methods in Java

Question

I have this question about the performance of a method in Java with a variable number of parameters.

Say I have the following 2 alternatives:

public          


        

Answer 1

I had the same question, and turned to experimentation.

public class ArgTest {

  int summation(int a, int b, int c, int d, int e, int f) {
    return a + b + c + d + e + f;
  }

  int summationVArgs(int... args) {
    int sum = 0;
    for (int arg : args) {
      sum += arg;
    }
    return sum;
  }

  final static public int META_ITERATIONS = 200;
  final static public int ITERATIONS = 1000000;

  static public void main(String[] args) {
    final ArgTest at = new ArgTest();
    for (int loop = 0; loop < META_ITERATIONS; loop++) {
      int sum = 0;
      final long fixedStart = System.currentTimeMillis();
      for (int i = 0; i < ITERATIONS; i++) {
        sum += at.summation(2312, 45569, -9816, 19122, 4991, 901776);
      }
      final long fixedEnd = System.currentTimeMillis();
      final long vargStart = fixedEnd;
      for (int i = 0; i < ITERATIONS; i++) {
        sum += at.summationVArgs(2312, 45569, -9816, 19122, 4991, 901776);
      }
      final long vargEnd = System.currentTimeMillis();
      System.out.printf("%03d:%d Fixed-Args: %d ms\n", loop+1, ITERATIONS, fixedEnd - fixedStart);
      System.out.printf("%03d:%d Vargs-Args: %d ms\n", loop+1, ITERATIONS, vargEnd - vargStart);
    }
    System.exit(0);
  }

}

If you run this code on a modern JVM (here 1.8.0_20), you will see that the variable number of arguments cause overhead in performance and possible in memory consumption as well.

I'll only post the first 25 runs:

001:1000000 Fixed-Args: 16 ms
001:1000000 Vargs-Args: 45 ms
002:1000000 Fixed-Args: 13 ms
002:1000000 Vargs-Args: 32 ms
003:1000000 Fixed-Args: 0 ms
003:1000000 Vargs-Args: 27 ms
004:1000000 Fixed-Args: 0 ms
004:1000000 Vargs-Args: 22 ms
005:1000000 Fixed-Args: 0 ms
005:1000000 Vargs-Args: 38 ms
006:1000000 Fixed-Args: 0 ms
006:1000000 Vargs-Args: 11 ms
007:1000000 Fixed-Args: 0 ms
007:1000000 Vargs-Args: 17 ms
008:1000000 Fixed-Args: 0 ms
008:1000000 Vargs-Args: 40 ms
009:1000000 Fixed-Args: 0 ms
009:1000000 Vargs-Args: 89 ms
010:1000000 Fixed-Args: 0 ms
010:1000000 Vargs-Args: 21 ms
011:1000000 Fixed-Args: 0 ms
011:1000000 Vargs-Args: 16 ms
012:1000000 Fixed-Args: 0 ms
012:1000000 Vargs-Args: 26 ms
013:1000000 Fixed-Args: 0 ms
013:1000000 Vargs-Args: 7 ms
014:1000000 Fixed-Args: 0 ms
014:1000000 Vargs-Args: 7 ms
015:1000000 Fixed-Args: 0 ms
015:1000000 Vargs-Args: 6 ms
016:1000000 Fixed-Args: 0 ms
016:1000000 Vargs-Args: 141 ms
017:1000000 Fixed-Args: 0 ms
017:1000000 Vargs-Args: 139 ms
018:1000000 Fixed-Args: 0 ms
018:1000000 Vargs-Args: 106 ms
019:1000000 Fixed-Args: 0 ms
019:1000000 Vargs-Args: 70 ms
020:1000000 Fixed-Args: 0 ms
020:1000000 Vargs-Args: 6 ms
021:1000000 Fixed-Args: 0 ms
021:1000000 Vargs-Args: 5 ms
022:1000000 Fixed-Args: 0 ms
022:1000000 Vargs-Args: 6 ms
023:1000000 Fixed-Args: 0 ms
023:1000000 Vargs-Args: 12 ms
024:1000000 Fixed-Args: 0 ms
024:1000000 Vargs-Args: 37 ms
025:1000000 Fixed-Args: 0 ms
025:1000000 Vargs-Args: 12 ms
...

Even at the best of times, the Vargs-Args never dropped to 0ms.