Time complexity of System.arraycopy(…)?

Question

System.arraycopy(Object src, int srcPos, Object dest, int destPos, int length) is a native method.

What is the time complexity for this method?

Answer 1

I did some investigation and later decided to write a test code, here is what I have.

My testing code is given below:

import org.junit.Test;

public class ArrayCopyTest {

  @Test
  public void testCopy() {
    for (int count = 0; count < 3; count++) {
      int size = 0x00ffffff;
      long start, end;
      Integer[] integers = new Integer[size];
      Integer[] loopCopy = new Integer[size];
      Integer[] systemCopy = new Integer[size];

      for (int i = 0; i < size; i++) {
        integers[i] = i;
      }

      start = System.currentTimeMillis();
      for (int i = 0; i < size; i++) {
        loopCopy[i] = integers[i];
      }
      end = System.currentTimeMillis();
      System.out.println("for loop: " + (end - start));

      start = System.currentTimeMillis();
      System.arraycopy(integers, 0, systemCopy, 0, size);
      end = System.currentTimeMillis();
      System.out.println("System.arrayCopy: " + (end - start));
    }
  }

}

It produces result shown below

for loop: 47
System.arrayCopy: 24

for loop: 31
System.arrayCopy: 22

for loop: 36
System.arrayCopy: 22

So, Bragboy is correct.