7. Interfaces

Polymorphism is available not only via inheritance (as discussed in the preceding chapter), but also via interfaces. Unlike abstract classes, interfaces cannot include any implementation. Like abstract classes, however, interfaces define a set of members that callers can rely on being implemented.

By implementing an interface, a type defines its capabilities. The interface implementation relationship is a “can do” relationship: The type can do what the interface requires an implementing type to do. The interface defines the contract between the types that implement the interface and the code that uses the interface. Types that implement interfaces must declare methods with the same signatures as the methods declared by the implemented ...

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