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Re: Why not String compare?

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On 8/26/2016 12:00 PM, Eric Douglas wrote:
> This seems odd, the String class returns false if you pass a null into equals(), but throws NPE if you pass null into compareTo().
> The Javadoc on it's compareTo() doesn't mention nulls much less NPE.
> The Javadoc on Comparator mentions it'll return NPE by default for a null, but any time I write a custom Comparator I return 1 for compareTo() if argument is null.

     Are you talking about Comparator, or about Comparable?  The
latter has a compareTo() method, the former does not.

     If you're speaking of Comparable, I think you're in violation
of the spec.  In

	ComparableThing x = ...;  // non-null
	ComparableThing y = null;
	int xy = x.compareTo(y);
	int yx = y.compareTo(x);

... you don't get xy and yx with opposite signs, as required by
the Comparable documentation:

	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.)

     If you're speaking of Comparator, simply returning 1 when either
argument of compare() is null is also a breach.  Consider

	Thing x = ...;  // non-null
	Thing y = null;
	Comparator<Thing> c = ...;
	int xy = c.compare(x, y);
	int yx = c.compare(y, x);

Again, you must ensure that sgn(xy) = -sgn(yx), but if both are 1
this doesn't hold.  (You should also arrange that c.compare(null,null)
returns 0, not 1 or -1.)

-- 
esosman@comcast-dot-net.invalid
The Tooth Fairy has gone high-tech, now pays in Bitecoin.

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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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