Week 5: Class hierarchies/01A. Class hierarchies

Often, when programming an object, you come across a situation where 2 classes have COMMON FEATURES. 
An example could be the classes Teacher and Student. 
Both classes would have at least the attributes name and email. 

However, in addition to the common attributes, 
the classes would also have separate attributes: 
for example, a teacher would not have an attribute for the number of credits, and 
a student would not have an attribute for the course being taught.


It is of course possible to create 2 separate classes with similar attributes. 
However, it would often make more sense to use class hierarchies in such a situation.

The idea of a class hierarchy is that classes can have DESCENDANTS and corresponding PARENTS (or "ancestors"). 
A class inherits characteristics from its parent. 
If a class has multiple children, they all share certain common characteristics. 
In addition to these, the children may, of course, have their own characteristics that are different from one another.

In addition to the client-supplier relationship discussed earlier, 
the inheritance relationship is another important relationship in object oriented programming





Parent and child classes
If class A inherits class B, 
class A is said to be a child class of B. 
Similarly, B is the parent class of A.

The following figure illustrates the inheritance relationships:
![image/png](https://cdn-uploads.huggingface.co/production/uploads/63d885f607cd1aa3c4a3ea30/rKFwQ-CFoRmxpILfjoDqS.png)

In the picture, for example
- A Vehicle is a superclass of the categories Car and Motorcycle
- The classes Hatchback and Truck are subclasses of the class Car
- All other classes inherit the properties of the 'Vehicle' classes: 
for example, Car and Motorcycle are both vehicles, but they also have their own, different properties.


The inheritance relationship therefore means that the inheriting class is also a parent class. 
For example, a hatchback is also a car and a vehicle. 

Thus, the class Dog could naturally inherit the class Animal, 
but the class Cat could not inherit the class Dog (because a dog is an animal, but a cat is not a dog). 

Similarly, the class Paperback could inherit the class Book, 
but the class Page could not (paperback is a book, page is not a book, even though a book has pages).