Comparator/Comparators API change proposal

[Henry Jen]

Hi,

Static interface method support has being available for a while, it
seems reasonable to move a couple methods from Comparators into Comparator.

Also it is recommended to rename Function-variant comparing to according
primitive type to eliminate ambiguity for lambda cases like following,

<T,R> Comparator<T> comparing(Function<T,R> f);
<T> Comparator<T> comparing(ToIntFunction<T> f);

Comparator<String> c = comparing(s -> s.size());

So here is what we are proposing,

1. Move all Comparators.comparing to Comparator.comparing
2. Rename various comparing methods to comparing, comparingInt,
comparingLong and comparingDouble accordingly.
3. Same renaming apply to Comparator.thenComparing

Other than that, we have

1. move Comparators.naturalOrder() and reverseOrder() to Comparator.
Basically, static factory method should be in Comparator. Convenient
helper/combinator methods such as byKey/byValue should be in Comparators.
2. rename Comparator.reverseOrder() default method to reverse(), it's
simply reverse form of the comparator.
3. Add nullsFirst(Comparator cmp) and nullsLast(Comparator cmp) into
Comparators as helper function to wrap up a comparator to be null-friendly.

Specdiff can be found at

http://cr.openjdk.java.net/~henryjen/ccc/8009736.1/specdiff

Thoughts?

Cheers,
Henry