Higher Level (AHL) topic B3.2.5. A design pattern is a proven, reusable solution to a common design problem. This unit explains what a design pattern is, the three families they fall into, and the three patterns the course requires you to explain: singleton, factory and observer, and the problem each one solves.
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What is a design pattern?
A design pattern is a reusable blueprint of a proven solution to a recurring programming problem; it is a guideline, not actual code.
Patterns are not tied to one language, so they describe how to design a solution rather than giving you the finished code.
Each pattern is usually described by its intent, motivation, structure (a UML diagram) and a code example.
Patterns fall into three groups: creational (how objects are created), structural (relationships between objects) and behavioural (how objects communicate).
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1. What is a design pattern in object-oriented programming?
2. Which feature is essential to the singleton design pattern?
3. A program needs a common interface for its objects but wants each subclass to decide which specific object is created. Which pattern fits best?
4. Which pattern uses a publisher and a list of subscribers to keep objects informed of updates?
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