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

From:

markspace <-@.>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 09 Nov 2011 22:43:38 -0800

Message-ID:

<j9frqs$pbk$1@dont-email.me>

On 11/9/2011 7:11 PM, Eric Sosman wrote:

I'd be inclined to go with the inner class, or perhaps with a
wrapper if there's a reason you can't modify Dog. YMMV.

I wonder if it's possible to make something like a wrapper, where
instead of one per object you just have a singleton of special cases.

public class Dog {
   String name;
   String breed;
   float weight;

   DogComparisonStrategy compare;

   public boolean equals( Object o ) {
     return compare.equals( this, o );
   }

   public int hashcode() {
      return compare.hashcode( this );
   }

}

class CompareByWeight implements DogComparisonStrategy {

   public boolean equals( Dog d1, Object o ) {
     if( !(o instanceof Dog) ) return false;
     Dog d2 = (Dog) o;
     return d2.weight == d1.weight;
   }

   public int hashcode( Dog d ) {
     return Float.getFloatbits( d.weight );
   }
}

At least you might not need a million of the things, unlike wrapper.
Obviously, you have to be able to modify Dog for this to work.