Programming Classes, Objects, Methods & Attributes (OCR A Level Computer Science)

Programming Classes

• To program classes, you should already have a solid understanding of what classes in Object Oriented Programming (OOP) are.

How do you Define 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

Programming Objects

• To program objects, you should already have a solid understanding of what objects in Object Oriented Programming (OOP) are.

Defining an Object

Pseudocode

Pseudocode for the class 'person' and instantiating two objects

Java

//creating the person class

public class Person {

         // creating 4 attributes for the person class

    private String firstName;

    private String surname;

    private String dateOfBirth;

    private String hobbies;

    // Constructor -This creates objects of the person class

    public Person(String firstName, String surname, String dateOfBirth, String hobbies) {

        this.firstName = firstName;

        this.surname = surname;

        this.dateOfBirth = dateOfBirth;

        this.hobbies = hobbies;

    }

//Creating Objects (Instances) of the person class

Person person1 = new Person("Bob", "Jones", "06/10/1981", “E Sports”);

Person person2 = new Person("Jess", "Jones", "05/04/1980", “Astronomy”);

Python

#creating the person class

class Person:

        #Constructor -This creates objects of the person class     

    def __init__(self, firstName, surname, dateOfBirth, hobbies):

        self.firstName = firstName

        self.surname = surname

        self.dateOfBirth = dateOfBirth

        self.hobbies = hobbies

#Creating Objects (Instances) of the person class

person1 = Person("Bob", "Jones", "06/10/1981", "E Sports")

person2 = Person("Jess", "Jones", "05/04/1980", "Astronomy")

Programming Methods

• To program methods, you should already have a solid understanding of what methods in Object Oriented Programming (OOP) are.

Defining Methods

Pseudocode

Pseudocode for creating methods

Java

//Creating a public method called BankLeft

public void bankLeft() {

 // Code to make the aircraft bank left

    }

//Creating a private Method called BankLeft

public void bankLeft() {

 // Code to make the aircraft bank left

    }

Python

#Creating a public method called BankLeft

def bank_left(self):

        # Code to make the aircraft bank left

#Creating a private method called BankLeft

• In Python, there is no explicit access modifier for methods like "private" in Java.

• By convention, methods with a single leading underscore _ are considered private and should not be accessed directly from outside the class.

_def _bank_left(self):

        # Code to make the aircraft bank left

• It's important to note that even though the method is marked as private, it can still be accessed and invoked from outside the class. However, as a rule, other developers should treat it as private and avoid accessing it directly.

Programming Attributes

Pseudocode

Example of a created class, "Person", containing several attributes

Java 

public class Person {

    // Attributes for the person class

    private String name;

    private int age;

    private String gender;

    private String occupation;

    private boolean isMarried;

}

Python

In Python attributes are defined using the self keyword followed by the attribute name and its initial value.

class MyClass:

   def __init__(self, attribute1, attribute2):

      # Define attributes

      self.attribute1 = attribute1

      self.attribute2 = attribute2