Ace Java 2026: Rock Your 'Thinking in Java' Challenge!

Classes that implement an interface must provide implementations for all of the abstract methods declared in the interface. Option A is incorrect because interfaces do not have fields, they only have method signatures. Option C is incorrect because interfaces cannot be extended, they are implemented. Option D is incorrect because interfaces do not have default implementations, they only provide method signatures. Therefore, the correct answer is B, since implementing all the abstract methods in an interface is a key requirement for classes to conform to an interface.