What are alternatives to sealed classes and how do they compare?

Sealed classes in Java provide a way to restrict which classes can inherit from a given class. While they are a powerful feature, there are alternatives that can achieve similar encapsulation or abstraction. This article discusses various alternatives to sealed classes and compares their functionalities.

Alternatives to Sealed Classes

• Abstract Classes: Abstract classes can define abstract methods that must be implemented by subclasses. They can also contain some implementation. However, they do not restrict the set of subclasses in the same way sealed classes do.
• Interfaces: Interfaces allow for multiple inheritances and can define default methods, but they don’t restrict which classes can implement them.
• Final Classes: Declaring a class as final means it cannot be subclassed. This is a direct way to prevent inheritance but doesn't offer the flexibility of sealed classes.
• Composition Over Inheritance: Instead of extending classes, you can use composition to achieve code reuse and flexibility without the concerns of inheritance hierarchies.

Comparison of Alternatives

The choice between sealed classes and their alternatives largely depends on the specific use case:

• Flexibility: Sealed classes offer controlled flexibility, whereas abstract classes and interfaces provide more variability.
• Encapsulation: Final classes provide strong encapsulation but lack extensibility, while sealed classes maintain a balance between extensibility and encapsulation.
• Design Patterns: Using composition can lead to more maintainable and less tightly coupled code, which some developers might prefer over inheritance.