OOP and inheritance

We have seen how we can use other people's code by instantiating/creating objects from the classes of an API like Android. But this whole OOP thing goes even further than that.

What if there is a class that has loads of useful functionality in it but not exactly what we want? We can inherit from the class and then further refine or add to how it works and what it does.

You might be surprised to hear that we have done this already. In fact, we have done this with every single app we have created. When we use the extends keyword, we are inheriting. Remember this:

public class MainActivity extends AppCompatActivity ...

Here, we are inheriting from the AppCompatActivity class, along with all its functionality – or more specifically, all the functionality that the class designers want us to have access to. Here are some of the things we can do to classes we have extended.

We can even override a method and still rely in part on the overridden method in the class we inherit from...