Groups > comp.lang.java.programmer > #35527

Re: Why not String compare?

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From	Robert Klemme <shortcutter@googlemail.com>
Newsgroups	comp.lang.java.programmer
Subject	Re: Why not String compare?
Date	Wed, 31 Aug 2016 19:24:03 +0200
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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 - equivalence 
relation vs. total order.  You can reasonably say "that nothing is not 
equivalent to myself" while from "not equivalent" nothing follows for 
order.  And btw. the concept of treating null special is quite common, 
for example with RDBMS.

> It's not "symmetry" as such, that implied the requirement.  It was
> just pragmatically defined so for .compareTo while not for .equals.

Well, but that is the contract.  And I can see some sense in this.

> Any usecase for including null into the natural ordering of certain
> Comparable objects is just flawed.

There, now you said it yourself. :-)

Cheers

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

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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