Abstract class is a good choice when you are sure some methods are concrete/defined and must be implemented in the SAME WAY in all derived classes.
Normally we prefer Interface because it gives us the flexibility to modify the behavior at later stage.
Choosing between interfaces and abstract classes depends on the specific design requirements and the nature of the relationships between the classes in your application. Here are some guidelines to help you decide when to use an interface and when to use an abstract class in real applications:
Use Interfaces When:
- Multiple Inheritance of Behavior: If you need a class to inherit behavior from multiple sources (i.e., implement multiple contracts), use interfaces. Languages like C# allow a class to implement multiple interfaces, enabling it to provide various sets of behaviors.
- Polymorphism: When you want to achieve polymorphism, allowing objects of different classes to be treated uniformly through a common interface, use interfaces. This enhances code reusability and flexibility.
- Contracts and APIs: Use interfaces to define clear contracts and APIs that different components of your application must adhere to. Interfaces ensure a consistent way of interacting with objects and promote better communication among developers.
- Loose Coupling and Dependency Injection: Interfaces promote loose coupling between components, which is useful when implementing dependency injection patterns. They allow for easier swapping of implementations at runtime, making the application more flexible and maintainable.
- Unit Testing and Mocking: Interfaces are crucial for unit testing as they allow you to create mock objects that simulate behavior during testing. This isolates components and makes testing more efficient.
Use Abstract Classes When:
- Common Implementation: If you have a common implementation that you want to share among multiple related classes, use an abstract class. Abstract classes can provide concrete (non-abstract) methods that derived classes inherit, reducing code duplication.
- Partial Implementation: When you want to provide a partial implementation of a class (some methods with default behavior), use an abstract class. Derived classes can override these methods to customize their behavior.
- Designing for Future Extension: Abstract classes are useful when you want to design a class for future extension, where you anticipate having derived classes with specific implementations. The abstract class serves as a blueprint for these derived classes.
- Adding New Methods to Existing Classes: If you need to add new methods to existing classes without breaking their implementations, abstract classes are a better choice. You can add new abstract methods to the abstract class, and all derived classes will be required to implement them.
- Restricting Instantiation: Abstract classes cannot be instantiated directly, so if you want to prevent direct instantiation of a class and require it to be used as a base for other classes, use an abstract class.
Remember that in some cases, you can also use a combination of interfaces and abstract classes to achieve the desired functionality. Use interfaces to define common behaviors and abstract classes to provide shared implementation where appropriate.
Ultimately, the choice between interfaces and abstract classes should be based on the specific requirements and design goals of your application. Both concepts are valuable tools in creating well-structured, maintainable, and extensible software.
