Chapter 7 - Implementing Interfaces and Inheriting Classes

1. What is a delegate?

   • A delegate is a type-safe method reference. It can be used to execute any method with a matching signature.

2. What is an event?

   • An event is a field that is a delegate having the event keyword applied. The keyword ensures that only += and -= are used; this safely combines multiple delegates without replacing any existing event handlers.

3. How is a base class and a derived class related?

   • A derived class (or subclass) is a class that inherits from a base class (or superclass).

4. What is the difference between the is and as operators?

   • The is operator returns true if an object can be cast to the type. The as operator returns a reference if an object can be cast to the type; otherwise, it returns null.

5. Which keyword is used to prevent a class from being derived from, or a method from being overridden?

           sealed 
   

   • Find more information on the sealed keyword at https://msdn.microsoft.com/en-us/library/88c54tsw.aspx

6. Which keyword is used to prevent a class from being instantiated with the new keyword?

           abstract 
   

   • Find more information on the abstract keyword at https://msdn.microsoft.com/en-us/library/sf985hc5.aspx

7. Which keyword is used to allow a member to be overridden?

           virtual 
   

   • Find more information on the virtual keyword at https://msdn.microsoft.com/en-us/library/9fkccyh4.aspx

8. What's the difference between a destructor and a deconstructor?

   • A destructor, also known as a finalizer, must be used to release resources owned by the object. A deconstructor is a new feature of C# 7 that allows a complex object to be broken down into smaller parts.

9. What are the signatures of the constructors that all exceptions should have?

   • The following are the signatures of the constructors that all exceptions should have:

     • A constructor with no parameters

     • A constructor with a string parameter usually named message

     • A constructor with a string parameter, usually named message, and an Exception parameter usually named innerException

10. What is an extension method and how do you define one?

    • An extension method is a compiler trick that makes a static method of a static class appear to be one of the members of a type. You define which type you want to extend by prefixing the type with this.