IB Computer Science HL · Year 2 · Lesson 20

Design patterns + B3.2 checkpoint

Multiple-class OOP adds relationships and flexible behaviour through inheritance, polymorphism, abstraction, composition and patterns.

Paper 250 minutesB3.2.5 · B3.2.1 · B3.2.2 · B3.2.3 · B3.2.4
Today’s targets

What you need to be able to do

2 / 8
  • ExplainCommonly used design patterns in OOP
  • RetrieveReconnect today’s new material to previously taught content from this topic.
B3.2.5B3.2.1B3.2.2B3.2.3B3.2.4
Paper 2 lensMatch the depth of every response to the command term. Previously learned content can move quickly, but retrieval must still be accurate.
Retrieve

Rapid Recall Deck

3 / 8

Say the answer aloud before flipping. Mark secure knowledge quickly and spend time on the gaps.

  • What problem does the Singleton pattern address?: It ensures a class has a single shared instance and provides controlled access to it.
  • What problem does the Factory pattern address?: It centralizes object creation so calling code does not need to know every concrete class or construction detail.
  • What problem does the Observer pattern address?: It lets dependent objects be notified when another object's state changes.
  • Why are design patterns useful?: They provide reusable, well-known approaches to recurring software-design problems.
  • How are inheritance and polymorphism connected?: Inheritance can establish a common parent type, while polymorphism lets child objects provide different behaviour through that common type.
  • How is abstraction different from encapsulation?: Abstraction focuses on the essential interface and hides unnecessary complexity; encapsulation controls how state and behaviour are packaged and accessed.
B3.2.5 · Learn

Core knowledge and application

4 / 8
B3.2.5Explain

Commonly used design patterns in OOP

Multiple-class OOP adds relationships and flexible behaviour through inheritance, polymorphism, abstraction, composition and patterns.

Exam moveGive the mechanism or relationship and make the reasons/causes explicit.
Required detail 1The key design patterns such as singleton, factory and observer
Required detail 2The application of design patterns in solving recurring programming challenges
Assessment boundaryPaper 2

Explain it without notes

Explain: Commonly used design patterns in OOP in the context of a school platform with multiple interacting object types.

  • The key design patterns such as singleton, factory and observer
  • The application of design patterns in solving recurring programming challenges
Apply

Transfer to a new scenario

5 / 8
ScenarioA school platform with multiple interacting object types needs a design or technical decision related to today’s topic. Explain what matters and why.
  • The key design patterns such as singleton, factory and observer
  • The application of design patterns in solving recurring programming challenges
Exam lens

Paper 2 practice

6 / 8
Build the response before checking notesUse precise terminology and match the required depth.
  1. Explain: Commonly used design patterns in OOP in the context of a school platform with multiple interacting object types.
Self-checkAnswer the exact command term. For explain, include mechanism/reason; for compare, pair criteria; for discuss/evaluate/justify, build supported reasoning and a conclusion.
2027 Case Study

Generative AI research checkpoint

7 / 8

Build a reusable evidence bank for Paper 1 Section B. Keep claims technical, specific and supported.

Research checkpoint

Research GAN training balance: what happens when the discriminator or generator becomes too dominant?

Challenge focus: Explain why GAN training depends on a workable balance between generator and discriminator performance.

Homework

Finish the learning cycle

8 / 8

IA — main task

Continue Criterion D development. Keep code readable, record meaningful implementation decisions, and maintain testing/evidence notes as you work.

Syllabus — short

Complete one targeted Paper 2/Paper 1 retrieval task from today’s lesson.