What is the function of the 'implements' keyword in Java?

The 'implements' keyword in Java serves a specific purpose in object-oriented programming, particularly in the context of interfaces. When a class uses the 'implements' keyword, it is signaling that it is agreeing to adhere to the contract defined by an interface. This means that the class is committed to providing concrete implementations for all the abstract methods declared in the interface.

Using interfaces in Java allows for a form of multiple inheritance, where a class can implement multiple interfaces and thus inherit the behavior contracts set out by those interfaces. This promotes a design principle known as "programming to an interface," making it easier to create flexible and interchangeable code.

The other options provided do not accurately reflect the role of the 'implements' keyword. Defining a new method pertains to method declarations, indicating class inheritance relates more to the 'extends' keyword, and creating a new variable type does not involve the 'implements' keyword at all. Therefore, the function of the 'implements' keyword is to enforce contract adherence from an interface, allowing classes to guarantee that they fulfill the required behaviors defined by the associated interfaces.