Congratulations, you've completed the first level of the second quest! You learned about OOP and its four main pillars, and you played around with inheritance and encapsulation. And in the second level, you're working on understanding polymorphism, overloading, abstraction, and interfaces.

Upon completing this lesson, knowing what polymorphism is, you'll be able to settle parent-child problems, because you'll know what needs to be done if a child wants to use one of his forefathers' methods. In other words, you won't be confused by a whale with cow ancestry that can swim but lacks horns and a bell. You'll even be able to code one up.

To prevent barking by cats that have descended from a dog, you'll have to master polymorphism in practice! Diego won't let you get bored: it's time to complete tasks about whales, cows, dogs, and other Terran creatures. But mainly about cats, of course

All methods inside a class must have unique names. More specifically, the combination of a method's name and its set of parameter types must be unique. Imagine you need to write an Add() method to sum up two numbers. But you still aren't certain whether the numbers are ints or doubles. The smart thing to do is to overload the Add method. Rishi will explain everything else.

Just when you've learned a new topic, here comes Diego! But this can't help but please you. If you don't start working on tasks right away, you'll forget all these subtleties of method overloading before everything fully sinks in. So, carry on! Bang out five programs and send them to your mentor for review.

You often need to define something unspecific and basic. For example, a "car". It will have an engine and vehicle body. This isn't a car. It's only an abstraction—a class that we made for convenience. But you could use it to whip up a Ferrari or a Geo Metro. This lesson has the details. They are interesting.

A programmer's life and work are dangerous and full of abstractions. Abstract thoughts, abstract neighbors, abstract animals, and abstract girls. But we won't get into that last topic. Instead, let's do some more tasks involving abstract animals and their specific descendants with overloaded methods.

An interface is the legitimate child of Abstraction and Polymorphism. The interface is very much like an abstract class where all the methods are abstract. It is declared the same way as a class, but with the keyword interface. This lesson will teach you why we need them, and how and when to use them.

Imagine that you're a robotic builder. You have dozens of subordinate robots and each of them can have multiple skills. Suppose you need to urgently finish building a wall. You gather together all the robots that have the "builder" ability, and you tell them to build the wall. You don't care about the type of the robot. Even robotic watering cans are okay. If it knows how to build, let it build.

From the secret CodeGym center, Diego the Robot makes a promise: you'll sleep peacefully, but these peaceful nights must be earned. If you don't do these tasks about interfaces right now, they will come to you in your dreams… In short, it would be better to do them now. You shouldn't pick a fight with abstractions.

You've probably already guessed that Professor Hans Noodles doesn't give bad advice! This time he's found a link to an excellent lesson about polymorphism and interfaces. It will help you add some structure to your knowledge, if you want to. Think you already know everything? Read this lesson and you'll understand how very wrong you are.

Did you know that sometimes resting is good for you? Relax, kick back your chair, and watch an interesting video about a high-tech electric car. This isn't just entertainment. It's an important part of the comprehensive curriculum developed by the pedagogical board at the secret CodeGym center.