Inheritance (OOP) (OCR A Level Computer Science): Revision Note

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)