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From "Laurent Perez" <hak...@gmail.com>
Subject Re: [lang] equalsBuilder unexplained wrong equality with java.lang.Longs ?
Date Mon, 17 Dec 2007 13:34:07 GMT
Well... I of course agree my manual "==" instead of equals() was
wrong, but I guess nobody else has ever used EqualsBuilder with Long
fields... hard to believe, but hey.

Still, I find EqualsBuilder Javadoc and implementation misleading,
http://commons.apache.org/lang/api/org/apache/commons/lang/builder/EqualsBuilder.html#append(java.lang.Object,%20java.lang.Object)
says it will use equals() method on objects, but when objects are
Long, it does not.

Or maybe this is a known pitfall of EqualsBuilder, and I just went in,
but this is still very confusing.

laurent

2007/12/17, Shawn Garner <shawndgarner@hotmail.com>:
>
> I know there are tools/plugins to catch it.
> Personally I don't make those mistakes (I make different ones) anymore.
>
> It tends to be those who are new to Java or switch programming languages frequently.
> They are also not likely to use something like Findbugs.
>
> Nothing beats a compiler warning ;)
>
>
> Thanks,
> Shawn D. Garner
>
>
> > Date: Mon, 17 Dec 2007 12:58:22 +0000
> > From: sebbaz@gmail.com
> > To: user@commons.apache.org
> > Subject: Re: [lang] equalsBuilder unexplained wrong equality with java.lang.Longs
?
> >
> > 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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