Groups > comp.lang.java.programmer > #35529

Re: Why not String compare?

From	Andreas Leitgeb <avl@logic.at>
Newsgroups	comp.lang.java.programmer
Subject	Re: Why not String compare?
Date	2016-09-01 10:17 +0000
Organization	A noiseless patient Spider
Message-ID	<slrnnsg01f.456.avl@login.logic.tuwien.ac.at> (permalink)
References	(3 earlier) <e2bo9iF9m4nU1@mid.individual.net> <d9d392a6-7361-4743-aaef-22ec3d126722@googlegroups.com> <e2nb40F26seU1@mid.individual.net> <slrnnsd9q3.456.avl@login.logic.tuwien.ac.at> <e2oi5kFbhheU1@mid.individual.net>

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Robert Klemme <shortcutter@googlemail.com> wrote:
> On 31.08.2016 11:45, Andreas Leitgeb wrote:
>> Robert Klemme <shortcutter@googlemail.com> wrote:
>>> The implementor must ensure sgn(x.compareTo(y)) == -sgn(y.compareTo(x))
>>> for all x and y. (This implies that x.compareTo(y) must throw an
>>> exception iff y.compareTo(x) throws an exception.)
>> An equivalent "symmetry" could be expected from .equals, but isn't.
> Not necessarily since the underlying concept is different

That's not the point. If it *was* about symmetry (or anti- for compareTo)
then both compareTo and equals would have to throw NPE for null argument,
because obviously both throw NPE when called on a null reference.

> You can reasonably say "that nothing is not equivalent to myself"

If symmetry really was the requirement, then it would need to
include symmetry to null.equals(...).  It isn't, though.

That .compareTo(null) throws NPE is *not* "for symmetry", but for
a design decision, which defined compareTo to be NPE-symmetric.
For equals a different decision was made. And both these decisions 
still make sense.

I think, we're in "violent agreement" here, anyway.

Thread

Why not String compare? Eric Douglas <e.d.programmer@gmail.com> - 2016-08-26 09:00 -0700
  Re: Why not String compare? Robert Klemme <shortcutter@googlemail.com> - 2016-08-26 18:49 +0200
    Re: Why not String compare? Eric Douglas <e.d.programmer@gmail.com> - 2016-08-26 10:09 -0700
      Re: Why not String compare? Robert Klemme <shortcutter@googlemail.com> - 2016-08-26 22:48 +0200
        Re: Why not String compare? Eric Douglas <e.d.programmer@gmail.com> - 2016-08-26 13:55 -0700
          Re: Why not String compare? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-08-26 17:29 -0400
          Re: Why not String compare? Lew <lewbloch@gmail.com> - 2016-08-30 22:20 -0700
          Re: Why not String compare? Robert Klemme <shortcutter@googlemail.com> - 2016-08-31 08:17 +0200
            Re: Why not String compare? Andreas Leitgeb <avl@logic.at> - 2016-08-31 09:45 +0000
              Re: Why not String compare? Robert Klemme <shortcutter@googlemail.com> - 2016-08-31 19:24 +0200
                Re: Why not String compare? Andreas Leitgeb <avl@logic.at> - 2016-09-01 10:17 +0000
                Re: Why not String compare? Robert Klemme <shortcutter@googlemail.com> - 2016-09-02 18:29 +0200
  Re: Why not String compare? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-08-26 13:24 -0400
    Re: Why not String compare? Eric Douglas <e.d.programmer@gmail.com> - 2016-08-26 10:48 -0700
      Re: Why not String compare? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-08-26 14:50 -0400
        Re: Why not String compare? Eric Douglas <e.d.programmer@gmail.com> - 2016-08-26 12:19 -0700
      Re: Why not String compare? Lothar Kimmeringer <news200709@kimmeringer.de> - 2016-09-01 20:42 +0200
        Re: Why not String compare? Eric Sosman <esosman@comcast-dot-net.invalid> - 2016-09-01 17:57 -0400
    Re: Why not String compare? Eric Douglas <e.d.programmer@gmail.com> - 2016-08-26 11:03 -0700
      Re: Why not String compare? Lothar Kimmeringer <news200709@kimmeringer.de> - 2016-09-02 21:54 +0200

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