Revision Notes for IGCSE

Object-Oriented Programming (OOP)

1. Classes & Objects

A Class is a blueprint. An Object is an instance of that blueprint.

class Student:
    def __init__(self, name, id): # Constructor
        self.name = name  # Attribute
        self.id = id

# Creating an object (Instantiating)
student1 = Student("Nanjala", 101)

2. Encapsulation (Information Hiding)

Restricting access to data. In Python, we use a double underscore __ to make attributes Private. We then use Getters and Setters.

class Account:
    def __init__(self, balance):
        self.__balance = balance # Private attribute

    def get_balance(self): # Getter
        return self.__balance

3. Inheritance & Overriding

A child class "inherits" all methods from a parent class. Overriding happens when the child changes a parent method.

class User: # Parent
    def login(self):
        print("Logging in...")

class Admin(User): # Child
    def login(self): # Overriding
        print("Admin logging in with extra security...")

4. Containment (Aggregation/Composition)

This describes a "Has-a" relationship. One class contains an object of another class as an attribute.

class Engine:
    def start(self):
        pass

class Car:
    def __init__(self):
        self.my_engine = Engine() # Car CONTAINs an Engine

5. Overloading (Static Polymorphism)

Defining multiple methods with the same name but different parameters.
Note: Python does not support standard overloading natively like Java, but we simulate it with default arguments.

def add(a, b, c = 0):
    return a + b + c

print(add(5, 5))    # Uses 2 params
print(add(5, 5, 5)) # Uses 3 params

⚠️ Exam Note: Why use OOP?