Summary

Conclusions

Encapsulation hides an object’s state and exposes only a public contract, which lets a class guarantee its invariants. Access modifiers define visibility scopes: private is the class, internal is the assembly, public is any code, and the options involving protected relate to inheritance. A multi-project solution with a class library uses internal for hidden helper types. State is protected by properties with restricted setters, command methods, and defensive copies. Static members belong to the class: static fields are shared by all objects, a static constructor runs once, static classes group helper functions, and factory methods with private constructors provide clear ways to create objects.

Self-check questions

1. What is encapsulation? What is a class invariant?
2. Why are public fields considered bad practice?
3. What access modifiers exist in C#? What is the access scope of each?
4. What is the default access for class members and top-level types?
5. What is an assembly? How is the internal modifier related to assemblies?
6. How do you create a solution with a class library and a console application?
7. What is a defensive copy? When is it needed?
8. How do const, readonly, and static readonly differ?
9. What is a static field? Give examples of its use.
10. Why can’t a static method access instance fields?
11. When does a static constructor run?
12. What is a static class? What is the using static directive for?
13. What are factory methods and private constructors used for?
14. How are namespaces and project files organized?
15. Why is global mutable state dangerous?

Useful links

• Access modifiers: https://learn.microsoft.com/dotnet/csharp/programming-guide/classes-and-structs/access-modifiers
• Static classes and members: https://learn.microsoft.com/dotnet/csharp/programming-guide/classes-and-structs/static-classes-and-static-class-members
• Static constructors: https://learn.microsoft.com/dotnet/csharp/programming-guide/classes-and-structs/static-constructors
• The readonly keyword: https://learn.microsoft.com/dotnet/csharp/language-reference/keywords/readonly
• Class library in Visual Studio: https://learn.microsoft.com/dotnet/core/tutorials/library-with-visual-studio