abstract class Ancestor {
  //To count the family members of this Ancestor with givenColor eyes
  abstract int withColor(String givenColor);
}

class Unknown extends Ancestor {

  Unknown() { }

  //new Unknown().withColor("green") == 0
  //To count the family members of this Unknown with givenColor eyes
  int withColor(String givenColor) {
   // ...
   return 0;
  }
}

class Person extends Ancestor {
  String name;
  String eyeColor;
  Ancestor father;
  Ancestor mother;
  
  Person( String name, String eyeColor, Ancestor father, Ancestor mother) {
     this.name = name;
     this.eyeColor = eyeColor;
     this.father = father;
     this.mother = mother;
  }

  //new Person("Jim","brown",new Unknown(),new Unknown()).withColor("brown") == 1
  //new Person("Marge","blue",new Unknown(),new Person("Sam","brown",new Unknown(),new Unknown())).withColor("blue") == 1
  //To count the family members of this Person, including themselves, with givenColor eyes
  int withColor(String givenColor) {
    // ... this.name ... this.eyeColor ... this.father.AncestorMethod()
    //  ... this.mother.AncestorMethod()
    if ( this.eyeColor.equals(givenColor) )
      return 1 + this.father.withColor(givenColor) + this.mother.withColor(givenColor);
    else
      return 0 + this.father.withColor(givenColor) + this.mother.withColor(givenColor);
  }

}