Exam-style question
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A class diagram contains a single inheritance relationship, one composition relationship and one aggregation relationship. Explain how these three relationships differ, state the UML notation for the two whole-part relationships, and describe how polymorphism can be used in an object-oriented program involving inheritance.
Model answer
What a good answer should say
- Inheritance is a relationship in which one class derives from another class and can use or extend characteristics and behaviours from the other class.
- Composition is a whole-part relationship represented by a black diamond line in UML.
- Aggregation is also a whole-part relationship but is represented by a white diamond line.
- Polymorphism allows objects associated with related classes to respond through a common class-based relationship while providing class-specific behaviour.
Explanation
Why this works
The answer must distinguish inheritance from the two whole-part relationships, identify black diamond for composition and white diamond for aggregation, and connect polymorphism with related classes and class-specific behaviour. Mentioning overriding is relevant because it is an object-oriented concept in the specification and can support polymorphic behaviour.
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