Proposal: Comparables.isCommutativelyComparable (original) (raw)

Martin Buchholz martinrb at google.com
Sun Jun 9 01:52:40 UTC 2013

On Sat, Jun 8, 2013 at 8:50 AM, Doug Lea <dl at cs.oswego.edu> wrote:

Suppose you have two objects, x and y, both of the same type (x.getClass() == y.getClass()) and both known to be instanceof Comparable. Can you compare them? That is, can you safely call (Comparable)x).compareTo(y);

I'm surprised that this hasn't come up for consideration before. Or maybe I haven't noticed previous discussions?

Probably others tried and gave up, because you cannot actually get a reliable answer - you can only get YES NO DUNNO, because some of the generic type information you need may have been erased. My favorite example is:

<T extends Comparable> interface LexicographicList extends Comparable<List>, List

More information about the core-libs-dev mailing list