Is there any guarantee that the algorithm behind java.util.Collections.shuffle() remains unchanged in future Java releases?

Question

Is the following program guaranteed to produce a list with the same contents and ordering in future java releases?

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class Test {
  public static void main(String[] args) {
    List<String> list = new ArrayList<>(Arrays.asList("A", "B", "C", "D"));
    Collections.shuffle(list, new Random(42));
  }
}

The javadoc of the java.util.Random class guarantees that it will always return the same random numbers if intialized with the same seed in all future java releases.

But are there any guarantees regarding the algorithm behind the java.util.Collections.shuffle() utility function? The Javadoc for this utility function does not say anything about this.

I need this guarantee, because I want to be sure that persisted data will not be useless with any future java release.

Answer 1

There is no explicit guarantee, as you say.

On the other hand, the existence of a separate Collections.shuffle(List,Random) would suggest that the intention is that this method will always return the same order when invoked with a Random in an identical state. (This is useful to create repeatable tests for example.)

So it's a bit of a grey area.

But if core functionality depends on it and you want to be absolutely sure, you can implement the Fisher-Yates algorithm (or rather, the more efficient Durstenfeld algorithm) yourself, it's simple. It's so simple that it's definitely not worth taking the (probably small) risk that Collections.shuffle() will change in the future.