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

Objects (OOP)

What is an object?

• An object is a representation of a real-world entity eg teacher, aeroplane, mobile phone, cat etc

• A class is like a blueprint that describes the properties and behaviours of objects, while an object is a specific instance created based on that blueprint with its own unique values for the properties

• A constructor is a special method within a class that is automatically called when an object of that class is created  (instantiated)

• Constructors typically define the initial values of instance variables and perform any necessary setup to prepare the object for use

Example of 2 objects belonging to a class

Programming objects (OOP)

How do you program 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")