Just two questions

Thank you for taking your time and answering my questions thoroughly. So what you're saying is that the toString() method is automatically called every time we attempt to print from an object, but we do not see it. For this task, we override this toString()method when we call the println()method so that we can manually print the requirements "...is the cat's name. ... is the cat's father and ... is the cat's mother", am I correct? I think my third question was more for when passing Objects to the constructor's parameters. For example: Cat catDad = new Cat(dadName, catGrandma, catGrandpa). Do the program recognizes that we're passing catGrandma & catGrandpa objects and set Cat.grandma as catGrandma and set Cat.grandpa as catGrandpa?

with regards to the constructor: When you add arguments to the constructor it will match those arguments with the parameters of the constructor being used inside the class. It is important to know that the variable names that you use have 0 meaning to the computer and are only for helping humans understand. The thing that the computer understands is parameter types. Here is an example:

genericConstructor(int age, String name){
   this.age = age;
   this.name = name;
}

genericConstructor(int age, String address){
   this.age = age;
   this.address = address
}

Because these constructors have the same exact parameter types, this code would be illegal. You could argue that name and address are completely different things but to the computer both of these constructors (int, String), the variable names don't mean a thing above that. So in your example the only way that you could get the constructor to set the proper fields of grandpa and grandma is by passing in the arguments in the exact way that matches a constructor. So with your example above (dadname, catGrandMa, catGrandpa) is the constructor looked like this:

public Cat(String name, Cat grandpa, Cat Grandma){
     …..
}

The grandma and grandpa cats would be backwards in that cat object because that is the way you passed them into the constructor. The computer would not know the difference.

and regards to the println() method and toString(): Yes. If you commented out the code for the overridden toString() method and ran the code you would get the default toString() of the Object class being called and it will just print a jumble string 8 or 10 digits long that represented the spot in the computers memory where that object is stored.

Beautifully explained. I'll need to re-read the constructor explanation again. Thanks a ton man

If you haven't noticed yet constructors are basically methods. They both serve different purposes but are designed in the same fashion. As you go along with learning you will find a lot of similarities between seemingly different concepts. Once you start making those connections learning speeds up considerably.