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+13 votes
asked in CSC 305 Fall 2024 by (4.5k points)

3 Answers

+4 votes

A "has-a" relationship (composition) is better than an "is-a" relationship (inheritance) when the relationship between objects represents ownership or when the behavior of one object should not directly depend on another. "Has-a" is more flexible because it allows for modular, reusable components without tightly coupling classes. For example, if a Car class has a Engine class as a field, it reflects a "has-a" relationship since a car owns an engine, but an engine is not inherently a type of car. Composition also avoids the pitfalls of inheritance, such as inheriting unnecessary behaviors or violating the principle of single responsibility. By using "has-a," you can change or replace the associated object (Engine) without altering the parent object (Car), which promotes loose coupling and enhances code maintainability.

answered by (4.4k points)
+4 votes

Use a "has-a" relationship (composition) when:

  1. You want to reuse components across unrelated objects.
  2. You need modularity and encapsulation.
  3. Behavior or features may change or vary dynamically.
  4. The relationship is a part-whole rather than a strict subtype. (Bird has wings)

Use an "is-a" relationship when:

  1. Clear Hierarchy: The subclass is a specific type of the superclass (e.g., Dog is an Animal).
  2. Shared Behavior: The subclass shares common behavior with the superclass.
  3. Specialization: The subclass extends or modifies the superclass behavior.
  4. Static Relationship: The parent-child relationship is fixed.
  5. Code Reusability: Inherit common code to avoid duplication.
answered by (4.9k points)
0 votes

"is-a" is a very specific link between 2 classes. It's when there is a clear hierarchical relation between the 2: one is a "subtype" of the other. Like how a Square is a Rectangle. It is really focused on code extension and inheriting both fields and behavior. "Has-a" is way more flexible and rather than making you inherit code or specific implementation it just gives a general idea of what behavior a class is supposed to be able to do but is not specific as to how that is done.

answered ago by (4.1k points)
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