<<–2/”>a href=”https://exam.pscnotes.com/5653-2/”>p>Composition and Aggregation in object-oriented programming (OOP).
Introduction
Composition and Aggregation are two types of relationships between classes in OOP. They both express a “has-a” relationship, but the degree of dependency and lifetime management differs significantly.
Key Differences: Composition vs. Aggregation (Table Format)
| Feature | Composition | Aggregation |
|---|---|---|
| Relationship Type | “Part-of” | “Has-a” |
| Dependency | Strong. The child object’s lifecycle is entirely dependent on the parent object. | Weak. The child object can exist independently of the parent object. |
| Lifetime | Child object is created and destroyed with the parent object. | Child object may outlive the parent object. |
| Ownership | Parent object owns and manages the child object’s existence. | Parent object does not directly manage the child object’s existence. |
| Example | A car (parent) and its engine (child). The engine cannot exist without the car. | A department (parent) and its professors (child). Professors can exist independently of the department. |
| Memory Allocation | Child object’s memory is usually allocated within the parent object. | Child object’s memory may be allocated separately from the parent object. |
| UML Representation | Filled diamond symbol on the parent side of the relationship. | Empty diamond symbol on the parent side of the relationship. |
| Code Implementation | Child object is often instantiated within the parent’s constructor or a specific method. | Child object reference is passed to the parent object, often through a constructor or setter method. |
| Reusability | Less reusable, as the child object is tightly coupled to the parent. | More reusable, as the child object can be shared among multiple parent objects. |
Advantages and Disadvantages
| Type | Advantages | Disadvantages |
|---|---|---|
| Composition | – Clear ownership and responsibility. – Enforces encapsulation and data hiding. – Easier to reason about the system’s structure. | – Less flexible, as changes to the parent can significantly impact the child. – Less reusability of the child object. |
| Aggregation | – More flexible relationships. – Increased reusability of child objects. | – Less clear ownership and responsibility. – Potential for dangling references if not handled carefully. |
Similarities
- Both represent a “has-a” relationship between objects.
- Both help to model real-world relationships in code.
- Both are essential tools in object-oriented design.
FAQs on Composition and Aggregation
When should I use composition vs. aggregation?
- Use composition when the child object’s existence is strongly tied to the parent’s existence.
- Use aggregation when the child object can exist independently or be shared among multiple parents.
Can an object be both a part of another object and have its own independent existence?
- Yes, this can happen in complex scenarios where an object plays multiple roles.
How do I choose between composition and aggregation in my design?
- Consider the nature of the relationship between the objects. Does the child object’s existence depend on the parent? Does it make sense for the child to be shared?
Let me know if you’d like more examples or a deeper dive into specific code implementations!