inheritance-oop

Inheritance (OOP)

What is inheritance?

• Inheritance is a key concept in object-oriented programming (OOP) that allows a class to inherit the properties and behaviours (methods and attributes) of another class

• Inheritance promotes code reuse by allowing derived classes to inherit and utilise the existing code from the base class. This avoids duplicating code and promotes better organization and maintainability

• Inheritance establishes an “IS-A” relationship between the base class and the derived class

• For example, if you have a base class called Vehicle and a derived class called Car, you can say that “a Car is a Vehicle.”

• The car class inherits the properties and behaviours associated with being a vehicle

• Inheritance involves two main entities:

  • The base class (also known as the parent class or superclass) and the derived class (also known as the child class or subclass)

  • The derived class inherits the characteristics of the base class, meaning it can access and use the methods and attributes defined in the base class

Example of a base class and derived classes

• Base Class: The base class serves as the blueprint or template from which the derived class inherits 

  • It defines common properties and behaviours that can be shared among multiple derived classes

• Derived Class: The derived class inherits the attributes and methods of the base class

  • It can add additional attributes and methods

• If a car object was to be created, it may have the following attributes:

  • Manufacturer – The company that makes the car

  • Make -The model of the car

  • Cost – The price of the car to purchase

  • IsInsured – Whether or not the car is insured

  • EngineCapacity – The size of the engine for the car

• It may also have access to the following methods:

  • TurnEngineOn() – To start the car engine

  • TurnEngineOff() – To turn off the car engine

  • SteerLeft() – To turn the car to the left

  • SteerRight() – To steer the car to the left

  • GearChange() – To change the gear of the car

  • UnlockDoors() – To unlock the doors to the car

• The above methods are only a select few and there could be many more added for extra functionality

• In the following code, the super keyword is used in inheritance to refer to the superclass (Base class: Vehicles) and access its members (methods, attributes, or constructors) from within the subclass (Derived Class: Cars)

Programming inheritance

How do you program inheritance?

Pseudocode

Pseudocode for a class created using inheritance

Java

//vehicle class created public class Vehicle { //attributes created for the vehicle class private String manufacturer; private String make; private double cost; //constructor to create objects of type vehicle public Vehicle(String manufacturer, String make, double cost) { this.manufacturer = manufacturer; this.make = make; this.cost = cost; } //method to start the engine of the car public void turnEngineOn() { //code to turn the engine on } //method to stop the engine of the car public void turnEngineOff() { //code to turn the engine off } //method to steer the car to the left public void steerLeft() { // code to steer the vehicle left } //method to steer the car to the right public void steerRight() { // code to steer the vehicle right } } //Derived Class (Car) //the Car class uses the keyword 'extends' to inherit from the Vehicle class public class Car extends Vehicle { private boolean isInsured; private double engineCapacity; // Constructor to create objects of type Car public Car(String manufacturer, String make, double cost, boolean isInsured, double engineCapacity) { //the super keyword is used to inherit the attributes from the base class super(manufacturer, make, cost); this.isInsured = isInsured; this.engineCapacity = engineCapacity; } //method to change gear public void gearChange() { //code to change the gear of the car } //method to unlock the vehicle doors public void unlockDoors() { //code to unlock the doors of the car } }

Python

#Base class (Vehicle) #Vehicle class created class Vehicle: #attributes created for the Vehicle class def __init__(self, manufacturer, make, cost): self.manufacturer = manufacturer self.make = make self.cost = cost #method to start the engine of the car def turn_engine_on(self): # Code to turn the engine on #method to stop the engine of the car def turn_engine_off(self): # Code to turn the engine off #method to steer the car to the left def steer_left(self): # Code to steer the vehicle left #method to steer the car to the right def steer_right(self): # Code to steer the vehicle right #Derived Class (Car) #the Car class uses the keyword parent class name in parenthesis to inherit from the Vehicle class class Car(Vehicle): def __init__(self, manufacturer, make, cost, is_insured, engine_capacity): #the super keyword is used to inherit the attributes from the base class super().__init__(manufacturer, make, cost) self.is_insured = is_insured self.engine_capacity = engine_capacity #method to change gear def gear_change(self): # Code to change the gear of the car #method to steer the car to the right def unlock_doors(self): # Code to unlock the doors of the car