Java: Code Reading with Related Types

Abstract classes offer partial implementation; interfaces provide full abstraction.

Choosing between abstract classes and interfaces depends on your design needs. Abstract classes allow you to define some common behavior (method implementations) that can be shared by multiple subclasses, but a class can only inherit from one abstract class due to single inheritance. Interfaces, on the other hand, can be implemented by any class, allowing multiple inheritance of type. They define a contract without providing implementation, which is useful for defining capabilities that can be shared across unrelated classes. For instance, in an e-commerce domain, both 'Product' and 'Service' can implement a 'Purchasable' interface, defining a 'purchase()' method, without needing to share a common parent class.