General

  • An application’s architecture consists of following layers
    • UI layer: web app, wpf, windows gui, etc.
    • Business Logic: How your application works
    • Data Access Layer: Provides communication with the databases, e.g. EF Core, Repository Pattern
    • Common functionalities and libraries
    • Database

Classes

  • Explain classes and objects in simple terms
    • A class is a template that specifies the data and operations for an entity
    • An object is an instance of that class created at runtime using the new keyword
  • What is a static class? Why is it used?
    • A Static class provides a cohesive set of functionalities/services, and doesn’t contain any internal data
    • It has a static keyword in the signatures
    • It can only contain static members, i.e. static fields, static properties and static methods
    • It doesn’t have an instance constructor, as we don’t need to initialize it
    • It acts as a container for utility methods/common code libraries, e.g. logging, email, etc. 
  • What is a Partial class? 
    • Partial class allows us to split the definition of a class or a struct, an interface or a method over two or more source files.
  • What is a Sealed class?
    • A sealed class cannot be used as a base class.
    • No other classes can inherit a sealed class. 
  • Null conditional operator ?.
    • Removes the need to explicitly check the null references
    • If null then null; if not then dot
  • What is lazy loading and when would you use it?
    • It is a technique of instantiating objects when they are needed and not before
    • Create the instance in the property getter for the related object
  • What is an interface?
    • It’s a specification for identifying a related set of properties and methods.
    • When a class implements an interface, it commits to supporting that specification by implementing code
    • By using interfaces, we can write more generalized code when defining method parameters, or method return values

Fields and Properties

  • Why use Nullable field?
    • Use Nullable field, i.e. string price? to differentiate between not set and default value 
    • You can use HasValue and Value properties on nullable fields
  • What’s the difference in const vs readonly
    • const provides compile time constant values. They must be hardcoded, or an expression that evaluates at compile time. 
    • readonly provides runtime constant values. They can be set via expressions evaluated at runtime, but don’t change them later. 

Methods

  • How can you increase the readability of a method call?
    • Use the named arguments, i.e. placeOrder(product, quantity: 12, sendCopy: false)
  • What is a delegate?
    • A delegate is a type that represents a reference to a method with with a parameter and a return type
    • A lambda expression can be passed to a delegate
  • What are extension methods?
    • Extension methods enable you to "add" methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type.

Strings

  • Strings are immutable reference types, that act as value types
  • What’s verbatim string literals?
    • If you put @ in front of the string, it will print \r or \n as it is, instead of new line
  • How do you build large blocks of string?
    • Use StringBuilder, it’s a mutable string(conceptually)

Collections

  • What’s the difference in for vs. foreach in C#? 
  • foreach is easier to read and write
  • for gives us more flexibility. We can update the element, as well as change the order or sequence of iteration

Generics

  • What are generics? Why are they used?
    • Generics is a technique that allows to define variable data types
    • Generics allow us to write more reusable code without fixing data types, and at the same time provide type safe collections