Совсем запутался (((( . Подскажите какую тему (темы) еще раз посмотреть. И направьте на путь правильный. Спасибо

package com.javarush.task.task06.task0621; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; /* Родственные связи кошек */ public class Solution { public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String grandFatherName = reader.readLine(); Cat catGrandfather = new Cat(grandFatherName); String grandMotherName = reader.readLine(); Cat catGrandMother = new Cat(grandMotherName); String fatherName = reader.readLine(); Cat catFather = new Cat(fatherName, catGrandfather); String motherName = reader.readLine(); Cat catMother = new Cat(motherName); //, grandMotherName); String sonName = reader.readLine(); Cat catSon = new Cat(sonName, catMother, catFather); String daughterName = reader.readLine(); Cat catDaughter = new Cat(daughterName, catMother, catFather); System.out.println(catGrandfather); System.out.println(catGrandMother); System.out.println(catFather); System.out.println(catMother); System.out.println(catSon); System.out.println(catDaughter); } public static class Cat { private String name; private Cat grandfather; private Cat grandmother; private Cat mother; private Cat father; private Cat son; private Cat daughter; Cat(String name) { this.name = name; } Cat(String name, Cat grandfather) { this.name = name; this.grandfather = grandfather; } Cat(String name, Cat mother, Cat father) { this.name = name; this.mother = mother; this.father = father; } @Override public String toString() { // if (grandfather == null) { // return "The cat's name is " + name + ", no mother, no father"; // } else if (grandmother == null) { // return "The cat's name is " + name + ", no mother, no father"; // } if (grandfather == null) return "The cat's name is " + name + ", no mother " + grandfather; else if (grandfather != null ){ return "The cat's name is " + grandfather + " +" + grandmother + " " + " ddd " + mother; //+ father.name + " "; //+ mother.name; //father.name + ", no mother, father is " + grandfather; } else if (father != null){ return " " + father.name; } else return "The cat's name is " + name + ", mother is " + mother.name + " " + father.name; } } } // The cat's name is дедушка Вася, no mother, no father // The cat's name is бабушка Мурка, no mother, no father // The cat's name is папа Котофей, no mother, father is дедушка Вася // The cat's name is мама Василиса, mother is бабушка Мурка, no father // The cat's name is сын Мурчик, mother is мама Василиса, father is папа Котофей // The cat's name is дочь Пушинка, mother is мама Василиса, father is папа Котофей