Chapter 58 - Use of Object-Oriented Programming (OOP)

Question 1

What is Object-Oriented Programming?

Answer 1

Object-Oriented Programming (OOP) attempts to capture data, information and related functionality (code) to form structured items known as objects.

In OOP, the world is viewed as a collection of objects.

Question 2

What are objects and what can they be.

Answer 2

Objects are instances of classes (defined in the main body). They can be anything: from specific things such as cars and planes, to more abstract things such as bank accounts or data structures (stacks).

Question 3

Object features

Answer 3

Objects have their own attributes, states and methods (behaviours)

Question 4

Attributes

Answer 4

Attributes are variables or data members that belong to a class and represent its characteristics or state

Question 5

State

Answer 5

A state of an object is represented by its attributes e.g the radio is on/off

Question 6

Methods/Behaviours

Answer 6

Actions performed by an object (think of them like subroutines) often by altering attributes.

Question 7

What is a class?

Answer 7

A class is a blueprint/template for an object and it defines the attributes and behaviours (methods) of objects in that class.

These attributes are defined as the instance variables within a class.

Question 8

Sections of a class

Answer 8

1. Name of the class
2. The attributes: all the information shared with any object of this class type. Like variables.
3. The methods/behaviours: the code associated with the class that allows you to change/access its attributes. Like subroutines

Question 9

Information hiding

Answer 9

As a general rule, attributes/instance variables are defined as private whereas most methods are defined as public. This allows other classes to access the methods but not see/change the attributes.

Therefore objects need to use messages to interact with with another object’s state.

Question 10

What is a constructor?
What does the spec say about constructors?

Answer 10

A constructor initialises the attributes within a class.
Constructors are procedures with the name new. E.g def __init__ new (someAttributes).

Question 11

Instantation

Answer 11

An instance of a class - the creation of an object
They have the name new when object is created. E.g my_dog = new Dog(someArguments)

Question 12

Access the attribute “name” from the object my_dog. Then print it

Answer 12

print(my_dog.name)

Question 13

Make the dog bark using the “bark” method. Then print

Answer 13

print(my_dog.bark())

Question 14

Messages

Answer 14

Messages can either be getter or setter messages. In some languages, getter messages are written as functions (returning the value you wanted to get) wheras setter messages are written as procedures (usually used to change the state of the object).

Question 15

Summary of OOP

Answer 15

Each object belongs to a class
All objects of the same class have the same structure and methods but they have their own data
Objects belonging to a class are instances of that class.

Question 16

Encapsulation

Answer 16

This is where an object encapsulates its states (value of attributes/instance variables) and its behaviours/methods into a single entity so the attributes/behaviours of one object can’t affect those of the other.

Question 17

Inheritance

Answer 17

Classes can inherit attributes and methods from a parent class. A child in OOP is known as a subclass and a parent class is known as a superclass

Question 18

A car class inherits the attributes of a vehicle class. What would this look like?

Answer 18

class Vehicle:
def __init__new(self,doors,price):
self.doors = doors
self.price = price

class Car(Vehicle):
def __init__new(self,doors,price,wheels):
super().__init__(doors,price)
#super.new(doors,price)
self.wheels = wheels

Question 19

Polymorphism

Answer 19

Polymorphism enables methods to do different things based on the object they are acting upon. An example is overriding.

Question 20

Overriding

Answer 20

Overriding: defining a method with the same name and formal argument types as a method inherited from a superclass.

Question 21

Polymorphism example

Answer 21

class Animal:
def __init__ new (self,sound):
self.sound = sound

def makeSound(self):
pass

class Dog(Animal)
def__init__ new (self,sound):
super().__init__ new (sound)

def makeSound(self):
return f”The Dog goes {self.sound}”