What is the purpose of an interface in Java? To provide a concrete implementation of methods. To define a contract for classes to implement. To hide data within a class. To create objects directly.

The purpose of an interface in Java is: **To define a contract for classes to implement.** An interface specifies a set of methods that a class must implement, but it does not provide concrete implementations of those methods. This allows for a form of abstraction and enables multiple classes to implement the same interface in different ways, promoting polymorphism. The other options are incorrect for the following reasons: - **To provide a concrete implementation of methods:** Interfaces do not provide concrete implementations; they only declare methods. - **To hide data within a class:** Data hiding is achieved through access modifiers (like private) in classes, not through interfaces. - **To create objects directly:** Interfaces cannot be instantiated directly; they must be implemented by classes that can then be instantiated.