Hi Adrián,

The problem is that NSGA2 expects to be working with Fitness objects that
are specifically of type NSGA2Fitness (which is itself a subclass of

If you have your CustomFitness class inherent from NSGA2Fitness instead of
MultiObjectiveFitness, you should be good to go.


On Sun, Dec 9, 2018 at 4:38 PM Adrián Romero Cáceres <
[log in to unmask]> wrote:

> Hello!
> I have implemented a new betterThan operator into a CustomFitness class,
> which is an extended class of MultiObjectiveFitness.  I wrote
> pop.subpop.0.species.fitness = ec.multiobjective.CustomFitness inside my
> experiment param file. Once the execution starts, after the first
> generation fails, returning the next error:
> Exception in thread "main" java.lang.ClassCastException:
> ec.multiobjective.CustomFitness cannot be cast to
> ec.multiobjective.nsga2.NSGA2MultiObjectiveFitness
>          at
> ec.multiobjective.nsga2.NSGA2Breeder.assignFrontRanks(NSGA2Breeder.java:185)
>          at
> ec.multiobjective.nsga2.NSGA2Breeder.buildArchive(NSGA2Breeder.java:121)
>          at
> ec.multiobjective.nsga2.NSGA2Breeder.loadElites(NSGA2Breeder.java:82)
>          at ec.simple.SimpleBreeder.breedPopulation(SimpleBreeder.java:225)
>          at
> ec.multiobjective.nsga2.NSGA2Breeder.breedPopulation(NSGA2Breeder.java:113)
>          at
> ec.simple.SimpleEvolutionState.evolve(SimpleEvolutionState.java:104)
>          at ec.EvolutionState.run(EvolutionState.java:482)
>          at ec.Evolve.main(Evolve.java:771)
> I forgot something? Is it the right way to extend the betterThan operator?
> Thanks in advance,
> Adrián.


Doctoral Candidate, George Mason University