B3.2 Fundamentals of OOP for multiple classes: notes and practice

What you need to know

Our summary of the topic in our own words, not the IB guide. Points marked HL are for Higher Level only.

• Explain inheritance and the relationship between a superclass and a subclassHL
• Write code that defines a subclass and reuses superclass behaviourHL
• Design a class hierarchy for a described domain and justify where each behaviour belongsHL
• Explain polymorphism and how the same call can behave differently by object typeHL
• Write code that overrides a superclass methodHL
• Distinguish overriding from overloadingHL
• Explain abstraction in an object oriented design and what an abstract class or interface is forHL
• Decide whether a given concept should be an abstract class, an interface or a concrete classHL
• Distinguish composition from aggregation and from inheritanceHL
• Model a has-a relationship between classes and show it on a UML diagramHL
• Describe common design patterns and the problem each one solvesHL
• Recognise where a design pattern would improve a described designHL

Practice questions

Original questions written for the 2027 course, marked as you go. Easiest first.

• Inheritance and polymorphism with reference booksWritten · Stretch

Exam tips for B3.2

• Overriding replaces a method in a subclass, while overloading reuses a name with different parameters.
• Use "is-a" for inheritance and "has-a" for composition or aggregation when justifying a design.
• Show relationships on UML diagrams with the right arrows and multiplicities.