Interview Questions - Notes

What is MVC?

• Design pattern, separation of concerns between Model, View, and Controller.
• Model: data, View: UI, Controller: Interface between View and Model and accepts requests that eventually navigate to individual pages.
• Provide example.

What is MVC Routing?

• Allows for navigation by entering a URL into a browser, mapping the browser request to the controller action, and returning the corresponding page.
• Default MVC routing is based on the pattern "Controller/Action/ID".
• Controller - the controller that will handle the request.
• Action - The action method in the controller.
• ID - Optional, but when present the ID can be used to query data.

What are the SOLID Principles?

• coding design techniques intended for understandability, flexibility, and maintainability.
• Single responsibility.
  • a class should have only one job.
• Open/closed.
  • objects should be open for extension but closed for modification.
• Liskov substitution.
  • every subclass or derived class should be substitutable for their base or parent class.
• Interface segregation.
  • a class should not implement an interface that it doesn't use.
• Dependency inversion.
  • Entities must depend on abstractions, not concretions. This allows for decoupling. 

What is abstraction?

• The process of hiding certain details and showing only essential information to the user.
• Can be achieved with either abstract classes or interfaces.

What is an interface?

• A type definition similar to a class, except it purely represents a contact between an object and the user.
• A collection of method and property declarations.
• It can neither be directly instantiated as an object nor can member data be defined.

What is boxing and unboxing in C#?

• Boxing - assigning a value type variable as a reference type variable.
• Unboxing - assigning a reference type variable as a value type variable.

What is data encapsulation?

• Aka data hiding, implementation details of a class are hidden from the user.
• User can only perform a restricted set of operations on the hidden members of the class by executing methods.

What is dependency injection?

• A design pattern of achieving Inversion of Control (IoC) between classes and their dependencies.
• When a service (dependency object) is created outside of its client (the object that depends on it) that service can be passed into, or injected, into the client, typically through the client's constructor.

What is inheritance?

• Way to reuse base code of existing objects.
• At least 2 classes: base class (parent) and derived class (child).
• A derived class inherits the attributes and methods of the base class.

What is LINQ?

• Language-Integrated Query.
• Query capabilities integrated directly into C#, used to query both database sets and IQueryable collections. 

What is polymorphism?

• The ability to process objects in different wats depending on the data type or class.
• Two types of polymorphism:
  • Compile-time polymorphism - overloading methods.
  • Runtime polymorphism - overriding methods.
• The ability to work with different classes via the same interface is called polymorphism.
• Example:
  • Overload: AddHistoryAsync() of BTTicketHistoryService.
  • Override: GenerateClaimsAsync() of  BTUserClaimsPrincipalFactory .

What is Razor Syntax?

• A markup syntax that lets you embed server-based code (C#) into web pages.
• Generally have a .cshtml file extension.
• Code with Razor syntax is not rendered to the client.

What is the difference between a Class and an Object?

• Class:
  • A class is a user defined blueprint from which objects are created.
  • A class combines fields and methods into a single unit.
• Object:
  • A block of memory that has been allocated and configured according to a class.
  • An object is an instance of a class, and a program may create many objects of the same class.

What is the difference between an interface and an abstract class?

• An interface is not a class, it contains member declarations only.
• An abstract class can have declarations and implementations.
• Members of an interface must be public, abstract classed may contain private members.
• Multiple interfaces can be implemented by a class.
• A single abstract class can be inherited by a non-abstract class.

What is the difference between authentication and authorization?

• Authentication securely identifies users for application access.
• Authorization allows/denies securely identified users to access certain areas of the software.
• A user must be authenticated to be authorised.

What is the difference between overloading and overriding a method?

• Overloading:
  • creating methods with the same name but differ parametrically.
• Overriding:
  • re-writing a method, keeping the original signature, that has been inherited from a parent class.

In C# what are public, private, static, and void?

• Public: Access modifier for types and type members. Most permissive access level, there are no restrictions.
• Private: Access modifier, least permissive. Only accessible within the body of the class or struct they are declared in.
• Static: Globally accessible without creating an instance of a class.
• Void: A type modifier that identifies a method as having no return value. in async methods this is declared with the keyword Task instead of void.

What are some access modifiers in C#?

• Public: can be accessed from any code in the project.
• Private: can only be accessed by the code in the containing class.
• Protected: can be accessed by any method in the inherited classes and within the same class. Cannot be applied to classes and interfaces.
• Internal: access is restricted to classes within the current project assembly.
• Protected internal: access restricted to the current assembly and to types derived from the containing class in any assembly.
• Private protected: can only be accessed by the containing class and classes derived from the containing class within the same assembly.

What are value and reference types?

• Value types are stored in the stack (memory) and contain actual values of the data.
  • int, enum, byte, decimal, double, float, long, bool.
• Reference types contain references (memory addresses) that point to the location of the data represented by the variable. Reference types are stored in the heap, so when they are no longer used they can be marked for garbage collection and reuse.
  • string, class, interface, object.

What is a Try/Catch/Finally block?

• A coding technique used to trap exceptions at runtime.
• Code in the Try block tries to execute and if an exception is thrown the Catch block intercepts the error.
• If a Finally block is present the code within will always execute regardless of the Try/Catch result.