guava-libraries - Is the Ordering class thread safe?

Question

The guava-libraries have a class Ordering. I'm wondering if it's thread safe.

For example, can it be used as a static variable?

public static Ordering<String> BY_LENGTH_ORDERING = new Ordering<String>() {
   public int compare(String left, String right) {
      return Ints.compare(left.length(), right.length());
   }
};

Answer 1

It's as thread-safe as your compare method.

Default implementation of Ordering does not have any instance data, so the only thing that matters is how you define your compare method.

Answer 2

Yes, Ordering objects are all immutable unless you do something to make them mutable, such as extending Ordering and adding mutable fields, or providing a mutable Comparator in the from(Comparator) method or a mutable Function in onResultOf(Function).

But typically, you'd really have to go out of your way to make one that isn't thread safe.