Programming Classes, Objects, Methods & Attributes

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

Worked Example

Below is a sample of code for the class “Lizard”.

class Lizard
   private speed
   private mass
   private size
   public procedure new(givenSpeed, givenMass, givenSize)
      speed=givenSpeed
      mass=givenMass
      size=givenSize
   endprocedure
   public function breakBlock(brick)
      if speed*mass>=brick.getStrength() then
         speed=((speed*mass)-brick.getStrength())/mass;
         return true
      else
         return false
      endif
   endfunction

...
...
...
endclass

Identify an attribute in the Lizard class.

[1 marks]

How to answer this question to get full marks:

• There are 3 attributes in the Lizard class which are speed, mass and size

Answer:

Speed