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

Polymorphism (OOP)

What is polymorphism?

• In A Level Computer Science, polymorphism is a concept in programming that allows objects to take on different forms or behaviours.

• Different objects can share the same name or behaviour but can work in different ways

• It helps make code more flexible, reusable, and easier to maintain

• It allows flexibility and reusability in programming, making it easier to write and manage code

• Objects can be treated as belonging to a common group, even if they belong to different classes, making your code more versatile and adaptable to changes

Example 1 – method overloading

Method Overloading Example 1

• In the example above, all three classes all have a method named move(). Polymorphism allows methods to be declared with the same name but execute different code (in this case printing different messages)

• The override keyword Is used to provide a new implementation for a method that is already defined in the parent class (base class)

Example 2 - method overriding

Method Overriding Example 2

• In the above example, both the Motorcycle class and the Car class inherit from the base class Vehicle

• Objects from the Motorcycle and Car classes can call the startEngine() method, which will output "Engine Started!"

• If either of the object types calls the displayInfo() method, the program will execute the method from the object’s class, as it overrides the method from the Vehicle class

• For example:

  • If a Motorcycle object calls the displayInfo() method, "I am a Motorcycle!" will be output

  • If a Car object calls the displayInfo() method, "I am a Car!" will be output

Treating objects as common groups

• Polymorphism also allows objects of different classes to be treated as objects of a common superclass or base class

• For example:

  • Vehicle vehicle1 = new Car()

  • Vehicle vehicle2 = new Motorcycle()

• This allows an array of type Vehicle to store both Motorcycle and Car objects rather than in separate data structures

  • If the vehicle1.displayInfo() method is called, it will still output "I am a Car!"

  • If the vehicle2.displayInfo() method is called, it will still output "I am a Motorcycle!"

• This flexibility provided by polymorphism are essential for creating more maintainable and modular code