B3 Object oriented programming

For the new IB Diploma Computer Science syllabus to start teaching in August 2025, and for first examinations in May 2027.

Unit and lesson overviews will be gradually published as developed.

Lesson 1: Introducing OOP

B3.1.1 Evaluate the fundamentals of OOP.

Model real-world entities using OOP concepts: classes, objects, inheritance, encapsulation, polymorphism
The advantages and disadvantages of using OOP in various programming scenarios

B3.1.2 Construct a design of classes, their methods and behaviour.

Classes and their methods, based on application requirements
The use of unified modelling language (UML) class diagrams to represent class relationships, attributes and methods, to aid effective software design and planning

B3.1.4 Construct code to define classes and instantiate objects.

How to define classes and create objects from those classes
The role of constructors in initializing an object’s state, setting initial values for its attributes to define its condition or characteristics at the time of creation

B3.1.5 Explain and apply the concepts of encapsulation and information hiding in OOP.

The principles of encapsulation and information hiding
Apply access modifiers such as private and public
Controlling access to class members
The importance of limiting access to maintain the integrity and security of an object’s state

B3.1.3 Distinguish between static and non-static variables and methods.

The differences between static and non-static variables and methods, including their usage and scope
When to use instance variables instead of class variables, and how to apply these concepts effectively in code

B3.2.1 Explain and apply the concept of inheritance in OOP to promote code reusability.

How inheritance enables a hierarchical relationship between parent and child classes
Extending existing classes, utilizing inheritance to reuse and extend functionalities
The impact of inheritance on access to parent class members with different access modifiers (private, public, protected, default)

B3.2.2 Construct code to model polymorphism and its various forms, such as method overriding.

The principle of polymorphism and how it contributes to code flexibility and reusability
How to implement dynamic polymorphic behaviour through mechanisms like method overriding
How to apply static polymorphic behaviour to maximize code efficiency

B3.2.3 Explain the concept of abstraction in OOP.

B3.2.4 Explain the role of composition and aggregation in class relationships.

How to design objects by leveraging smaller component objects through composition and aggregation
That aggregation implies that the subcomponents can function independently of the aggregating class, while in composition, the subcomponents are tightly coupled and cannot exist outside the aggregating class