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

Inheritance vs Composition: Delving into the Differences and Implementing Composition in Java

In object-oriented programming, understanding the distinction between inheritance and composition is crucial. While inheritance represents an "is-a" relationship, denoting that one class is a specialization of another, composition reflects a "has-a" relationship, where one class contains an instance of another class as a field.

Refuting the Equivalence of Composition and Inheritance

Contrary to popular belief, composition and inheritance are fundamentally different. Composition models a "has-a" dependency, where one class contains another as a component, while inheritance creates an "is-a" dependency, establishing a parent-child hierarchy.

Practical Implementation of Composition in Java

Implementing composition in Java is straightforward. Instead of extending another class, create an instance of that class as a field within your current class. For instance, consider a hypothetical Stack class that could utilize composition:

class Stack {
    private List<Object> elements;

    public Stack() {
        elements = new ArrayList<>();
    }
    // Implementation of stack methods...
}

In this example, the Stack class composes a List, as opposed to extending the List class. This allows for greater flexibility and decoupling, ensuring that Stack is not bound to a specific implementation of the List interface.

Conclusion

Preferring composition over inheritance in object-oriented design promotes flexibility and reusability. If the relationship between two classes can be described as "has-a" rather than "is-a," composition should be the preferred approach. Additionally, referring to resources such as "Effective Java 2nd Edition" by Josh Bloch can provide valuable insights into best practices for object-oriented design.

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