Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.java.programmer > #9844

Re: equals(), Sets, Maps, and degrees of equality

Show all headers | View raw

Sean Mitchell <sean@mitchwood.com> wrote:
> Anyone ever run into the case where you wish an Object could have
> more than one equals(), or that Set and Map implementations would
> let you pass in something like a closure to determine key equality?

Yep, I also noticed this lack in the context of "orthogonality".
I just still haven't found any actual practical use for it.

> It seems to me that objects can be equal in varying degrees. Let's
> consider a class Dog:
> public class Dog {
>   String breed;
>   String name;
>   String age;
> }
> I may want to have a Set<Dog>, which holds only one Dog of each breed,

In that case, I'd use a Map<String,Dog>, which would be keyed by the breed
name itself, rather than by an arbitrary dog of that breed.

Probably, I'd even create a class Breed, that would encapsulate some more
properties along with the name, and then use the Breed class as key.

For the example at hand, this would allow filling the structure with breeds
that are "requested" (initially associated with null Dog), then some other
part of the code could pick an appropriate Dog for each requested Breed.

> But I may also want a Map<Dog, Owner> in which each Dog is made unique
> by name.

That doesn't make sense to me, because the owner would rather be a property
of the dog(*), than of its name. Who's the owner of "any dog called Rufus", btw?

*: natural language is sometimes quite at odds with modelling language. :-)

Back to comp.lang.java.programmer | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

equals(), Sets, Maps, and degrees of equality Sean Mitchell <sean@mitchwood.com> - 2011-11-09 18:33 -0800
  Re: equals(), Sets, Maps, and degrees of equality Owen Jacobson <angrybaldguy@gmail.com> - 2011-11-09 22:10 -0500
    Re: equals(), Sets, Maps, and degrees of equality v_borchert@despammed.com (Volker Borchert) - 2011-11-10 04:42 +0000
  Re: equals(), Sets, Maps, and degrees of equality Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-09 22:11 -0500
    Re: equals(), Sets, Maps, and degrees of equality markspace <-@.> - 2011-11-09 22:43 -0800
      Re: equals(), Sets, Maps, and degrees of equality Sean Mitchell <sean@mitchwood.com> - 2011-11-10 06:33 -0800
        Re: equals(), Sets, Maps, and degrees of equality markspace <-@.> - 2011-11-10 07:21 -0800
          Re: equals(), Sets, Maps, and degrees of equality Sean Mitchell <sean@mitchwood.com> - 2011-11-10 07:29 -0800
            Re: equals(), Sets, Maps, and degrees of equality markspace <-@.> - 2011-11-10 10:27 -0800
            Re: equals(), Sets, Maps, and degrees of equality Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-10 20:58 -0500
              Re: equals(), Sets, Maps, and degrees of equality markspace <-@.> - 2011-11-10 19:07 -0800
                Re: equals(), Sets, Maps, and degrees of equality Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-10 23:24 -0500
                Re: equals(), Sets, Maps, and degrees of equality markspace <-@.> - 2011-11-10 20:55 -0800
              Re: equals(), Sets, Maps, and degrees of equality Sean Mitchell <sean@mitchwood.com> - 2011-11-11 10:27 -0800
                Re: equals(), Sets, Maps, and degrees of equality Lew <lewbloch@gmail.com> - 2011-11-11 14:21 -0800
    Re: equals(), Sets, Maps, and degrees of equality Sean Mitchell <sean@mitchwood.com> - 2011-11-10 06:31 -0800
      Re: equals(), Sets, Maps, and degrees of equality Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-11-10 11:27 -0800
  Re: equals(), Sets, Maps, and degrees of equality Roedy Green <see_website@mindprod.com.invalid> - 2011-11-10 16:01 -0800
  Re: equals(), Sets, Maps, and degrees of equality Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-11-11 09:08 +0000
    Re: equals(), Sets, Maps, and degrees of equality Lew <lewbloch@gmail.com> - 2011-11-11 07:27 -0800
      Re: equals(), Sets, Maps, and degrees of equality Sean Mitchell <sean@mitchwood.com> - 2011-11-11 10:28 -0800
        Re: equals(), Sets, Maps, and degrees of equality Lew <lewbloch@gmail.com> - 2011-11-11 14:22 -0800
          Re: equals(), Sets, Maps, and degrees of equality markspace <-@.> - 2011-11-11 15:19 -0800
          Re: equals(), Sets, Maps, and degrees of equality Lew <lewbloch@gmail.com> - 2011-11-13 21:18 -0800
            Re: equals(), Sets, Maps, and degrees of equality Lew <lewbloch@gmail.com> - 2011-11-16 09:15 -0800

csiph-web