What characteristic is unique to interfaces compared to classes?

• A. Interfaces cannot have methods
• B. Classes can implement interfaces
• C. Interfaces can have multiple inheritance
• D. Classes can have abstract methods only

Answer: (C)

The uniqueness of interfaces compared to classes lies in their ability to support multiple inheritance. In Java, a class cannot inherit from more than one class due to the potential complexity and ambiguity that arises with multiple inheritance. However, a class can implement multiple interfaces, allowing for greater flexibility in designing software architecture.

This feature of interfaces allows a class to adopt behavior and contracts from multiple sources, which is particularly useful in designing systems that need to adhere to various specifications or functionalities. For instance, if you have an interface for 'Readable' and another for 'Writable', a single class can implement both, thereby inheriting the capabilities defined by both interfaces.

This capability is fundamental to Java's approach to interface design and promotes the use of abstraction and polymorphism, helping to achieve a more modular and testable codebase. In contrast, classes cannot have multiple inheritance relationships due to the common pitfalls associated with it, thereby reinforcing the distinctiveness of interfaces in this regard.