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

Methods (OOP)

What is a method?

• Methods are fundamental in object-oriented programming (OOP) and are functions associated with objects or classes that define the behaviour and actions that objects can perform

• There are two main types of methods:

  • A function

    • A function performs a task and returns a value

  • A procedure

    • A procedure performs a task buts does nor return a value

• For example, there are many different types of aircraft which all differ in design, but all require a ‘take off’ and ‘landing’ method

• An example of an aircraft class with both attributes and methods is shown below:

Example class for "aircraft" containing several methods

• Each object that is created from the aircraft class will have:

  • A manufacturer value to determine the company that created the aircraft

  • A model name for the type of aircraft

  • A value for passenger capacity to determine how many people it can carry

  • A speed value to determine its maximum speed

• Any objects that are created for the aircraft class also have access to the following Methods:

  • A take off method to get the plane airborne

  • A land method to land the plane safely

  • A bank left method to allow the plane to turn to the left

  • A bank right method to allow the plane to tur to the right

• As you can imagine, for an aircraft there would be many more methods that could be implemented such emergency landing and altitude cruising actions

• Once objects have been created, they can use the methods from within their class by using the dot (.) notation

• As these methods are associated with objects, they are called instance methods

• For example if an object has been created as below:

  • jumboJet = new aircraft (“Boeing”, ”747”, 416, 547)

• It can use methods by doing the following:

  • Objectname.Methodname:

  • For example:    jumboJet.Takeoff()

Public and private methods

• When declaring methods, it is important to determine how they can be accessed:

Programming methods (OOP)

How do you program a method?

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