How should I map long to int in hashCode()?

Question

I have a range of objects that have a long field whose value uniquely identifies a particular object across my entire system, much like a GUID. I have overriden

Answer 1

It's a bit of a minor thing if you're not using Guava already, but Guava can do this for you nicely:

public int hashCode() {
  return Longs.hashCode(id);
}

That gives you the equivalent of Long.valueOf(id).hashCode():

return (int) (value ^ (value >>> 32));

Additionally, if you were to have other values or objects that were part of the hashcode, you could just write

return Objects.hashCode(longValue, somethingElse, ...);

The long would be autoboxed into a Long so you'd get the correct hashcode for it as part of the overall hashcode.