Question

I am using ECJ (an evolutionary algorithms package) and I want to call certain variables that are in an extended class but I can’t figure out how to get to them from the problem class.

As you can see in the problem class below I want to be able to call the variable x in the NetworkGene class but it doesn’t work because I end up in the VectorGene class in which I can only call variable y.

class Problem {
  double fitness = 0;
  public void evaluate(final Individual ind){
    if(!(ind. instanceOf GeneVectorIndividual)){
      state.output.fatal("Not a GeneVectorIndividual",null);
    }
    fitness = 0;
    for(){
      fitness += ind.genome[i].x;
    }      
  }
}

public abstrabct class VectorIndividual extends Individual{
}

public class GeneVectorIndividual extends VectorIndividual{
  VectorGene[] genome;
}

public abstract class VectorGene implements Prototype {
  double y;
}

public class NetworkGene extends VectorGene{
  double x;
}

Answer 1

Classic polymorphism problem.

The quick and dirty solution is this: in the for loop in class Problem, add these lines

if (ind.genome[i] instanceof NetworkGene) {
    fitness += ((NetworkGene) ind.genome[i]).x;
}

But probably there’s a design problem you need to solve:

Why is ind.genome an array of VectorGenes instead of NetworkGenes?

What does x represent? Is there something you could express within VectorGene like a method getSomeValue() which in NetworkGene you would implement to return x (and in other subclasses you’d implement it to return some other appropriate value)?

Do you really need the inheritance relationship between VectorGene and NetworkGene – does it relate to some difference that you actually need to exploit in the problem you are currently trying to solve? Couldn’t you just have a single class containing properties x and y?