What is the main difference between a class and an interface in Java?

The primary distinction between a class and an interface in Java lies in their functionality and purpose. A class is a blueprint for creating objects and can provide both data (fields) and behavior (methods), meaning a class can have implemented methods that contain functionality. This characteristic allows a class to define how objects of that type behave.

On the other hand, an interface is essentially a contract that defines a set of abstract methods without providing any implementation. Interfaces are used to specify behaviors that classes must implement if they agree to the contract. The lack of implementation in an interface implies that it cannot directly provide behavior; rather, it relies on implementing classes to provide the actual functionality.

This key difference highlights the role of classes as complete structures providing behavior and data, while interfaces act as a way to enforce a set of behaviors across multiple classes without dictating how those behaviors should be implemented.