Re: default equals function?

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

--- BBBS/Li6 v4.10 Dada-1
* Origin: Prism bbs (1:261/38)
--- Synchronet 3.16a-Win32 NewsLink 1.98
Time Warp of the Future BBS - telnet://time.synchro.net:24

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).

--- BBBS/Li6 v4.10 Dada-1
* Origin: Prism bbs (1:261/38)
--- Synchronet 3.16a-Win32 NewsLink 1.98
Time Warp of the Future BBS - telnet://time.synchro.net:24

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

--- BBBS/Li6 v4.10 Dada-1
* Origin: Prism bbs (1:261/38)
--- Synchronet 3.16a-Win32 NewsLink 1.98
Time Warp of the Future BBS - telnet://time.synchro.net:24

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

--- BBBS/Li6 v4.10 Dada-1
* Origin: Prism bbs (1:261/38)
--- Synchronet 3.16a-Win32 NewsLink 1.98
Time Warp of the Future BBS - telnet://time.synchro.net:24