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

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


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.