What is a key difference between an interface and an abstract class in Java?

• A. Interfaces can have non-abstract methods
• B. Abstract classes can implement interfaces
• C. Interfaces can contain non-final variables
• D. Abstract classes can extend multiple interfaces

Answer: (B)

The key difference that B highlights is that abstract classes in Java can implement interfaces. This means that an abstract class is allowed to provide concrete implementations for the methods defined in the interface it has implemented. This feature allows for a certain level of abstraction while still being able to provide the functionality of the given interface.

An abstract class can have both abstract methods (which do not have any body and must be implemented by subclasses) and concrete methods (which do have an implementation). This flexibility allows developers to create a base class with implemented methods for shared behavior, while still requiring subclasses to provide specific implementations for the abstract methods.

In contrast, while interfaces in Java can also have default methods (which are non-abstract), their primary purpose is to define a contract that implementing classes must fulfill. They serve as a mechanism for achieving multiple inheritance of type in Java, whereas a class can inherit from only one abstract class, if it chooses to do so.

The other options do not accurately capture the unique capabilities of interfaces versus abstract classes. For example, while interfaces now can have default methods (which may be considered non-abstract), this isn't included in the choices. Regarding variable declarations, interfaces can only have static final variables (constants). Lastly, while abstract classes cannot extend