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From sebb <seb...@gmail.com>
Subject Re: [lang] equalsBuilder unexplained wrong equality with java.lang.Longs ?
Date Mon, 17 Dec 2007 12:58:22 GMT
On 17/12/2007, Shawn Garner <shawndgarner@hotmail.com> wrote:
>
> This is the number one programming error I've seen (not the only one though).
>
> Most of the time it is controlling logic that never gets executed.
> I'm always curious as to why it is never caught and what it will do when fixed.

Try using Findbugs - that will report the error...

> The problem is other programming languages do compare this way.  As well as some expression
languages.
> IMO Java should treat "==" as "object.equals" on objects and introduce another operator
for object pointer comparison like ".="
>
> I don't think we'll ever see it though because it affects a lot of existing source code
making it not backwards compatible.
>
> Shawn D. Garner
>
>
> > From: GGregory@seagullsoftware.com
> > To: user@commons.apache.org; commons-user@jakarta.apache.org
> > Date: Mon, 17 Dec 2007 04:32:44 -0500
> > Subject: RE: [lang] equalsBuilder unexplained wrong equality with java.lang.Longs
?
> >
> > Hello Laurent:
> >
> > This behavior is 'normal'. The concepts of object equality (the equals() method)
and object identity (==) are different. The method ' equals()' defined in Object can be overridden
by subclasses and defines if an object is 'equal' to another. Long overrides the equals method
to check to see if the object passed in wraps the same primitive long value. OTOH, the ==
operator compares two object identities, that is, is the object on the left-hand side the
same object as the one on the right-hand side. Even though two objects instances may be semantically
equal (as in the example below), they are not the same object so fails the == comparison.
> >
> > For example:
> >
> > public class TestLongEquals extends TestCase {
> >
> >     public void testname() throws Exception {
> >         Long long1a = new Long(1);
> >         Long long1b = new Long(1);
> >         Assert.assertFalse(long1a == long1b);
> >         Assert.assertTrue(long1a.equals(long1b));
> >     }
> > }
> >
> > Gary
> > Seagull Software
> >
> > > -----Original Message-----
> > > From: Laurent Perez [mailto:hakimm@gmail.com]
> > > Sent: Sunday, December 16, 2007 3:17 PM
> > > To: Jakarta Commons Users List
> > > Subject: [lang] equalsBuilder unexplained wrong equality with java.lang.Longs
?
> > >
> > > Hi !
> > >
> > > I'm struggling with a problem I don't understand, my equalsBuilder's
> > > isEquals seem to return false when dealing with Longs :
> > >
> > > I have a bean class UiTheme, with a property private Long id.
> > >
> > > The following equals builder will return false when this.id = 1 and
> > > rhs.id =  1 :
> > >
> > >         public boolean equals(Object object) {
> > >                 if (!(object instanceof UiTheme)) {
> > >                         return false;
> > >                 }
> > >                 UiTheme rhs = (UiTheme) object;
> > >                 return new
> > > EqualsBuilder().appendSuper(super.equals(object)).append(this.id,
> > > rhs.id).isEquals();
> > >         }
> > >
> > > If I manually do the equality, as in this.id.equals(rhs.id), then it
> > > is true (because, well... 1 = 1 !)
> > > If I do an equality like this.id == rhs.id, then it is false (being a
> > > Java newbie... maybe it should be false, not sure if doing == instead
> > > of equals(obj) is correct with Longs)
> > >
> > > So I assume (am I wrong ?) that equalsBuilder's isEquals uses "=="
> > > instead of "equals(obj)"... but I really, really don't understand why.
> > >
> > > Can anyone enlighten me ?
> > >
> > > thanks !
> > > --
> > > <a href="http://in-pocket.blogspot.com">http://in-pocket.blogspot.com
> > > - Mobile world, technology and more</a>
> > >
> > > ---------------------------------------------------------------------
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> >
> >
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>
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