CS Notes

Inheritance (OOP)

3 min read

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 organisation 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
  • 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)

Example of a base class and derived classes Example of a base class and derived classes

Worked Example

The classes office and house inherit from building. Describe what is meant by inheritance with reference to these classes.

[2]

How to answer this question:

  • 1 mark per bullet up to a maximum of 2 marks, e.g:
    • When the child/derived/subclass class office/house takes on attributes/methods…
    • … from building / parent/base/superclass/ class

Answer:

Example answer to get full marks: When the derived classes “office” and “house” inherit attributes/methods [1] from the “building” base class, they gain access to the properties and behaviours defined in the “building” class. [1]

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