Composition vs. Inheritance in Java: When Should You Choose Which?

Understanding the Distinction between Inheritance and Composition

While inheritance and composition both involve relationships between classes, they serve distinct purposes. Inheritance establishes an "is-a" relationship, implying that one class inherits the attributes and behaviors of another, while composition represents a "has-a" relationship.

Composition in Java

To implement composition in Java, you can declare an instance of another class as a field of your current class instead of extending it. For instance, rather than extending the Vector class, the Stack class could have implemented composition by incorporating a Vector instance as its field.

Advantages of Composition

Composition offers several advantages over inheritance:

• Flexibility: Composition allows you to replace underlying data structures or implementations without breaking existing code, ensuring greater adaptability.
• Modularity: Compositions can be easily swapped out or replaced, making it easier to modify and maintain your codebase.
• Encapsulation: Composition allows you to access and modify the underlying elements individually, enhancing data integrity and control.

Josh Bloch's Recommendations

For guidance on effective object-oriented design, refer to Josh Bloch's authoritative book "Effective Java 2nd Edition." Specifically, his Item 16 emphasizes the preference for composition over inheritance, while Item 17 highlights the importance of designing and documenting for inheritance or prohibiting it altogether.

By prioritizing composition over inheritance, you can create more flexible, modular, and maintainable code.

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