B3.1 Fundamentals of OOP for a single class: notes and practice

What you need to know

Our summary of the topic in our own words, not the IB guide.

• Explain what object oriented programming is and how it differs from a procedural approach
• Distinguish a class from an object and explain what instantiation means
• Evaluate the benefits of an object oriented design for a described problem
• Identify the attributes and methods a class needs from a problem description
• Draw a UML class diagram for a single class showing attributes, methods and visibility
• Distinguish static from non-static variables and methods, and say which belongs to the class and which to the instance
• Predict the value of a static variable shared across several objects
• Write code that defines a class with a constructor
• Write code that instantiates objects and calls their methods
• Trace a program that creates several objects and state the state of each
• Explain encapsulation and information hiding and why internal state is protected
• Apply access modifiers to attributes and methods appropriately
• Write accessor and mutator methods, including validation inside a mutator

Learn it

• Class versus object; making an instance

  Lesson with 3 exercises

• Attributes and methods from a description

  Lesson with 2 exercises

Practice questions

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

• Class or objectWritten · Warm-up
• Greenhouse potWritten · Core
• Trace: two objectsTrace table · Core
• Trace: two objects (Java)Trace table · Core
• Classes, objects and encapsulation in Java and PythonWritten · Stretch
• Static counters and objects in a library classWritten · Stretch
• Ticket planWritten · Stretch

Exam tips for B3.1

• A class is the blueprint and an object is one thing made from it. Use the terms precisely.
• Static members belong to the class and are shared by every object. Trace them carefully.
• Put validation inside mutator (setter) methods. It is a common exam request.