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default equals function?

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  default equals function? "bob smith" <bob.smith@1:261/38.remove-t9h-this> - 2012-08-10 18:39 +0000
    Re: default equals function? "Eric Sosman" <eric.sosman@1:261/38.remove-t9h-this> - 2012-08-10 18:39 +0000
      Re: default equals function? "bob smith" <bob.smith@1:261/38.remove-t9h-this> - 2012-08-10 18:39 +0000
        Re: default equals function? "rossum" <rossum@1:261/38.remove-t9h-this> - 2012-08-10 18:39 +0000
        Re: default equals function? "Eric Sosman" <eric.sosman@1:261/38.remove-t9h-this> - 2012-08-10 18:39 +0000
    Re: default equals function? "Jeff Higgins" <jeff.higgins@1:261/38.remove-t9h-this> - 2012-08-10 18:39 +0000
      Re: default equals function? "Arne Vajhøj" <arne.vajhøj@1:261/38.remove-6gh-this> - 2012-08-10 19:41 +0000

#17636 — default equals function?

From: bob smith <bob@coolfone.comze.com>

Let's say I have a class like this:

public class Kern_Pair {
        int letter1, letter2;

}

Can someone tell me how the default equals function will behave?

like

kernpair1.equals(kernpair2)

?

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#17637

  To: bob smith
From: Eric Sosman <esosman@ieee-dot-org.invalid>

On 8/9/2012 5:58 PM, bob smith wrote:
> Let's say I have a class like this:
>
> public class Kern_Pair {
>       int letter1, letter2;
>
> }
>
> Can someone tell me how the default equals function will behave?
>
> like
>
> kernpair1.equals(kernpair2)
>
> ?

     Teachable Moment.

     The Kern_Pair class has no equals() method of its own, so it
inherits equals() from the nearest superclass that has one.  Walk up the class 
inheritance tree to find the nearest ancestor with an equals().  The class 
inheritance tree for Kern_Pair is fairly short: Its immediate superclass is 
Object (because you didn't say "extends SomethingElse"), so the equals() method 
for Kern_Pair *is* the equals() method of Object.

     Now all you need to do is go to the Javadoc and study what
Object's equals() will do.

--
Eric Sosman
esosman@ieee-dot-org.invalid

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#17641

  To: Eric Sosman
From: bob smith <bob@coolfone.comze.com>

On Thursday, August 9, 2012 5:11:07 PM UTC-5, Eric Sosman wrote:
> On 8/9/2012 5:58 PM, bob smith wrote:
>
> > Let's say I have a class like this:
>
> >
>
> > public class Kern_Pair {
>
> >     int letter1, letter2;
>
> >
>
> > }
>
> >
>
> > Can someone tell me how the default equals function will behave?
>
> >
>
> > like
>
> >
>
> > kernpair1.equals(kernpair2)
>
> >
>
> > ?
>
>
>
>      Teachable Moment.
>
>
>
>      The Kern_Pair class has no equals() method of its own, so it
>
> inherits equals() from the nearest superclass that has one.  Walk
>
> up the class inheritance tree to find the nearest ancestor with an
>
> equals().  The class inheritance tree for Kern_Pair is fairly short:
>
> Its immediate superclass is Object (because you didn't say "extends
>
> SomethingElse"), so the equals() method for Kern_Pair *is* the
>
> equals() method of Object.
>
>
>
>      Now all you need to do is go to the Javadoc and study what
>
> Object's equals() will do.
>
>
>
> --
>
> Eric Sosman
>
> esosman@ieee-dot-org.invalid

The equals method for class Object implements the most discriminating possible 
equivalence relation on objects; that is, for any non-null reference values x 
and y, this method returns true if and only if x and y refer to the same object 
(x == y has the value true).

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#17642

  To: bob smith
From: rossum <rossum48@coldmail.com>

On Fri, 10 Aug 2012 07:12:06 -0700 (PDT), bob smith
<bob@coolfone.comze.com> wrote:

>The equals method for class Object implements the most discriminating
>possible equivalence relation on objects; that is, for any non-null
>reference values x and y, this method returns true if and only if
>x and y refer to the same object (x == y has the value true).
Correct.  What do you think that means in practice for your Kern_Pair class?

As a minor point, the Java naming convention does not have underscores in class 
names: KernPair would be the expected name.  Kern_Pair looks more like C++ than 
Java.

rossum

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#17646

  To: bob smith
From: Eric Sosman <esosman@ieee-dot-org.invalid>

On 8/10/2012 10:12 AM, bob smith wrote:
> On Thursday, August 9, 2012 5:11:07 PM UTC-5, Eric Sosman wrote:
>> On 8/9/2012 5:58 PM, bob smith wrote:
>>> [...]
>>> Can someone tell me how the default equals function will behave?
>>  [...]
>>       Now all you need to do is go to the Javadoc and study what
>> Object's equals() will do.
>
> The equals method for class Object implements the most discriminating
possible equivalence relation on objects; that is, for any non-null reference 
values x and y, this method returns true if and only if x and y refer to the 
same object (x == y has the value true).

     ... and there you have it.  Any questions?

--
Eric Sosman
esosman@ieee-dot-org.invalid

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#17639

  To: bob smith
From: Jeff Higgins <jeff@invalid.invalid>

On 08/09/2012 05:58 PM, bob smith wrote:
> Let's say I have a class like this:
>
> public class Kern_Pair {
>       int letter1, letter2;
>
> }
>
> Can someone tell me how the default equals function will behave?
>
> like
>
> kernpair1.equals(kernpair2)
>
> ?
<http://docs.oracle.com/javase/tutorial/java/IandI/objectclass.html>
Here is a convenient dashboard to the Oracle Java documentation.
<http://docs.oracle.com/javase/7/docs/>
You may replace the 7 in the above address with a 3, 4, 5 or 6 to see older 
versions documentation.

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#17652

  To: Jeff Higgins
From: Arne Vajhoj <arne@vajhoej.dk>

On 8/9/2012 6:22 PM, Jeff Higgins wrote:
> Here is a convenient dashboard to the Oracle Java documentation.
> <http://docs.oracle.com/javase/7/docs/>
> You may replace the 7 in the above address with a 3, 4, 5 or 6
> to see older versions documentation.

And surprising that works (via redirect).

Surprisingly because Java SE 3 and 4 are J2SE 1.3 and 1.4!

Someone at Oracle has been smart.

Arne

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