Classes (OOP) (Cambridge (CIE) A Level Computer Science): Revision Note

Classes (Object-Oriented Programming)

What is a class?

• A class is a blueprint used to create objects in Object-Oriented Programming (OOP)

• It defines a structure for attributes (data) and methods (behaviour)

Key terms

Example

• A Student class could contain:

  • Attributes: name, dateOfBirth, gender

  • Each Student object (e.g. John, 06/10/2015, Male) has its own values

Prebuilt vs custom classes

• Below is a visual representation of both a class and objects that have been instantiated

• In the image, the identifiers are P1 and P2

Example of a class and objects

Programming classes (OOP)

How do you program a class?

• In this example we will:

  • Define a class for a car sales program where the following is required:

    • Name of Manufacturer

    • Model of Car

    • Price

    • Mileage

    • Whether the car is preowned

• Instantiate two objects for the car sales program ensuring that they have appropriate identifiers

• List two methods that would be useful for a car object

Pseudocode

Pseudocode for creating classes, a constructor, and functions

Java

//creating a class called cars

public class Cars {

//creating class attributes for a car

    private String Manufacturer;

    private String Model;

    private int Price;

    private int Mileage;

    private boolean PreOwned;

    //Constructor - This is used to create the objects. More on this in the object chapter)

    public Cars(String manufacturer, String model, int price, int mileage, boolean preOwned) {

        this.Manufacturer = manufacturer;

        this.Model = model;

        this.Price = price;

        this.Mileage = mileage;

        this.PreOwned = preOwned;

    }

    //method to make the car go faster.

    public void Accelerate(){

        //code to be executed which will make the car go faster

    }

    //Method to honk horn

    public void honkHorn(){

        // code to be executed which will honk the car horn

    }

}

Python

#creating a class called cars

class Cars:

    # constructor - This is used to create the objects. More on this in the object chapter)

    def __init__(self, manufacturer, model, price, mileage, preOwned):

        self.Manufacturer = manufacturer

        self.Model = model

        self.Price = price

        self.Mileage = mileage

        self.PreOwned = preOwned

       

    #method to make the car go faster.

    def Accelerate(self):

        # code to be executed which will make the car go faster

 

    # method to honk horn

    def honkHorn(self):

        # code to be executed which will honk the car horn