Is there any relation between the class that implements interface and that interface?
class-hierarchy, interface, java
Solution
Yes. The relationship is exactly the same
Book is a Taxable too.
EDIT
An interface is an artifact that happens to match Java's ( and probably C# I don't know ) `interface` keyword.
In OO interface is the set of operations that a class is 'committed' perform and nothing more. Is like a contract between the object class and its clients.
OO programming languages whose don't have `interface` keyword, still have class interface OO concept.
Problem
Consider this class hierarchy: - `Book extends Goods` - `Book implements Taxable` As we know, there is a relationship between a subclass and its superclass (is-a). Q: Is there any relationship like "is-a" between `Book` and `Taxable`? GOOD Answers, but you said that "is-a" is also a relationship between `Book` and `Taxable`, but "is-a" is a relation between classes, and an interface is not a class!