Re: Objects comparaison ?

From	dhtml <dhtmlkitchen@gmail.com>
Newsgroups	comp.lang.javascript
Subject	Re: Objects comparaison ?
Date	2011-10-15 21:28 -0700
Organization	http://groups.google.com
Message-ID	<d66a4e0d-c27d-4fcf-9e1d-74e15613d52a@t38g2000prg.googlegroups.com> (permalink)
References	(4 earlier) <1411612.7OFYzboFZ6@PointedEars.de> <ace50d65-1357-49c9-83da-cc72bddc4382@11g2000yqk.googlegroups.com> <2326223.jLKWLtnpvF@PointedEars.de> <e0b407d3-9663-4c23-9863-5969374eaa2d@e37g2000yqa.googlegroups.com> <2065619.34vx2sxqLb@PointedEars.de>

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On Oct 15, 12:37 pm, Thomas 'PointedEars' Lahn <PointedE...@web.de>
wrote:
> dhtml wrote:
> > Thomas 'PointedEars' Lahn wrote:
> >> dhtml wrote:
> >> > Thomas 'PointedEars' Lahn wrote:
> >> >> Jukka K. Korpela wrote:
> >> >> > 13.10.2011 22:21, Thomas 'PointedEars' Lahn wrote:
> >> >> >> Java's equals() method [– which exists precisely for that purpose –
> >> >> >> should provide a good start for an implementation in ECMAScript.]
>
> >> > Java `Object.equals` does nothing more than use Java's == which is
> >> > analagous to JavaScript's ===.
>
> >> I did not write `Object.equals()', if you cared to notice.
>
> > Which Java equals() method did you mean?
>
> Context matters.  By "should provide a good *start* for an implementation
> *in* ECMAScript" I was referring to the *concept* of Java's Object.equals()
> method, a method which is *overriden* by subclasses.
>
Not necessarily. Object `equals` method may be overridden but this is
often neglected by programmers. Java guidelines for how to override
`equals` are applicable here.

> The OP was wondering about the difference between comparing two object
> references and two primitive strings in an ECMAScript implementation.  
Two different String objects can never be == as they are different
objects. Two primitive strings may be == or ===. A primitive string
and a string object may be == but never ===.

var A1 = new String("a");
var A2 = new String("a");
var a = "a";

a  == A1; // true
a  == A2; // true
A1 == A2; // false

a === A1; // false

You know this, but not all readers will.

> Consider then, for example, String.equals(), which is necessary in Java
> because *there* *are* *no* *primitive* *string* *values* *in* *Java*, and
> `x == "foo"' would be useless (it would always result in `false').  

Not always. Depends if it'd been interned. But that's not relevant to
our discussion. Anyway:

So you
> need to do x.equals("foo") or – better¹ – "foo".equals(x) in Java [1] for
> what you need only `==' in ECMAScript.
>
Right because in Java, a null String `x`, where x.equals("foo") might
be a NPE.

> So comparing strings, for example, is more complicated in Java.  But by
> comparison ECMAScript's approach also is less powerful and less flexible
> because the way the comparison is performed there is more or less written in
> stone, defined by the algorithms in the Specification.
>
RIght.
--
Garrett

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Thread

Objects comparaison ? unbewusst.sein@fai.invalid (Une Bévue) - 2011-10-13 20:20 +0200
  Re: Objects comparaison ? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2011-10-13 21:47 +0300
    Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-13 21:21 +0200
      Re: Objects comparaison ? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2011-10-13 22:40 +0300
        Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-13 21:46 +0200
          Re: Objects comparaison ? dhtml <dhtmlkitchen@gmail.com> - 2011-10-13 13:11 -0700
            Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-14 01:26 +0200
              Re: Objects comparaison ? dhtml <dhtmlkitchen@gmail.com> - 2011-10-14 12:41 -0700
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-15 21:37 +0200
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-15 15:51 -0700
                Re: Objects comparaison ? dhtml <dhtmlkitchen@gmail.com> - 2011-10-15 21:28 -0700
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-16 11:41 +0200
                Re: Objects comparaison ? dhtml <dhtmlkitchen@gmail.com> - 2011-10-16 09:05 -0700
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-16 21:59 +0200
                Re: Objects comparaison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-17 10:53 +0100
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-17 07:02 -0700
                Re: Objects comparaison ? Andreas Bergmaier <andber93@web.de> - 2011-10-17 16:27 +0200
                Re: Objects comparaison ? dhtml <dhtmlkitchen@gmail.com> - 2011-10-17 21:28 -0700
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-18 11:12 +0200
                Re: Objects comparaison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-18 15:23 +0100
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-18 19:48 +0200
                Re: Objects comparaison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-19 17:08 +0100
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-20 23:58 +0200
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-20 15:46 -0700
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-18 10:55 +0200
                Re: Objects comparaison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-18 15:59 +0100
                Re: Objects comparaison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-18 19:33 +0200
                Re: Objects comparaison ? Scott Sauyet <scott.sauyet@gmail.com> - 2011-10-18 14:05 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-18 16:51 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-18 17:21 -0700
                Re: Objects comparaison ? Scott Sauyet <scott.sauyet@gmail.com> - 2011-10-19 04:40 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-19 16:41 -0700
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-19 17:14 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-19 18:33 -0700
                Re: Objects comparaison ? Scott Sauyet <scott.sauyet@gmail.com> - 2011-10-23 11:43 -0700
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-19 15:32 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-19 16:54 -0700
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-19 17:32 -0700
                Re: Objects comparaison ? "Michael Haufe (TNO)" <tno@thenewobjective.com> - 2011-10-19 18:39 -0700
                Re: Objects comparaison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-19 16:32 +0100
                Re: Objects comparaison ? Scott Sauyet <scott.sauyet@gmail.com> - 2011-10-19 14:18 -0700
                Re: Objects comparaison ? Antony Scriven <adscriven@gmail.com> - 2011-10-19 15:46 -0700
                Objects comparison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-20 16:28 +0100
                Re: Objects comparison ? Antony Scriven <adscriven@gmail.com> - 2011-10-20 12:23 -0700
                Re: Objects comparison ? Antony Scriven <adscriven@gmail.com> - 2011-10-20 15:04 -0700
                Re: Objects comparison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-21 15:38 +0100
                Re: Objects comparison ? Andreas Bergmaier <andber93@web.de> - 2011-10-22 19:40 +0200
                Re: Objects comparison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-23 11:49 +0100
                Re: Objects comparison ? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2011-10-24 19:00 +0200
                Re: Objects comparison ? Scott Sauyet <scott.sauyet@gmail.com> - 2011-10-21 05:29 -0700
                Re: Objects comparison ? John G Harris <john@nospam.demon.co.uk> - 2011-10-21 16:30 +0100
            Re: Objects comparaison ? Jukka Lahtinen <jtfjdehf@hotmail.com.invalid> - 2011-10-18 18:06 +0300
              Re: Objects comparaison ? Jake Jarvis <pig_in_shoes@yahoo.com> - 2011-10-18 17:43 +0200
      Re: Objects comparaison ? unbewusst.sein@fai.invalid (Une Bévue) - 2011-10-14 06:11 +0200
        Re: Objects comparaison ? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2011-10-14 08:07 +0300
          Re: Objects comparaison ? unbewusst.sein@fai.invalid (Une Bévue) - 2011-10-14 07:31 +0200
            Re: Objects comparaison ? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2011-10-14 08:59 +0300
              Re: Objects comparaison ? unbewusst.sein@fai.invalid (Une Bévue) - 2011-10-14 08:36 +0200
        Re: Objects comparaison ? unbewusst.sein@fai.invalid (Une Bévue) - 2011-10-14 08:35 +0200

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