We have seen how we can use other people's hard work by instantiating/creating objects from the classes of an API such as that of 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 quite 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 game and demo we looked at. When we use the extends keyword, we are inheriting, for example, in this line of code:

public class MainActivity extends Activity ...

Here, we are inheriting the Activity class along with all its functionality, or more specifically, all of 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 override a method and still rely in part on the overridden method in the class we inherit...