1. What's the difference between an interface and an abstract class?
- An abstract class is a class that is only partially implemented by the programmer. It may contain one or more abstract methods. An abstract method is simply a function definition that serves to tell the programmer that the method must be implemented in a child class.
- An interface is similar to an abstract class; indeed interfaces occupy the same namespace as classes and abstract classes. For that reason, you cannot define an interface with the same name as a class. An interface is a fully abstract class; none of its methods are implemented and instead of a class sub-classing from it, it is said to implement that interface.
- Abstract classes can have constants, members, method stubs and defined methods, whereas interfaces can only have constants and methods stubs.
- Methods and members of an abstract class can be defined with any visibility, whereas all methods of an interface must be defined as public.
- When inheriting an abstract class, the child class must define the abstract methods, whereas an interface can extend another interface and methods don't have to be defined.
