C# Linked in Answers

 

C#

Q1. In which of these situations are interfaces better than abstract classes?

•  When you need to define an object type's characteristics, use an interface. When you need to define an object type's capabilities, use an abstract class.
•  Interfaces are a legacy of older versions of C#, and are interchangeable with the newer abstract class feature.
•  When you need a list of capabilities and data that are classes-agnostic, use an interface. When you need a certain object type to share characteristics, use an abstract class.
•  You should use both an interface and an abstract class when defining any complex object.

Q2. Which statement is true of delegates?

•  Delegates are not supported in the current version of C#
•  They cannot be used as callbacks.
•  Only variables can be passed to delegates as parameters.
•  They can be chained together.

Official documentation: Delegates

Q3. Which choice best defines C#'s asynchronous programming model?

•  reactive
•  inherited callback
•  task-based
•  callback-based

Official documentation: Task asynchronous programming model

Q4. How would you determine if a class has a particular attribute?

•  .

var type = typeof(SomeType);
var attribute = type.GetCustomAttribute<SomeAttribute>();

•  .

var typeof(MyPresentationModel).Should().BeDecoratedWith<SomeAttribute>();

•  .

Attribute.GetCustomAttribute, typeof(SubControllerActionToViewDataAttribute)

•  .

Attribute.GetCustomAttribute(typeof(ExampleController), typeof(SubControllerActionToViewDataAttribute))

Official documentation: Attribute Class

Official documentation: Attribute.GetCustomAttribute Method

Q5. What is the difference between the ref and out keywords?

•  Variables passed to out specify that the parameter is an output parameter, while ref specifies that a variable may be passed to a function without being initialized.
•  Variables passed to ref can be passed to a function without being initialized, while out specifies that the value is a reference value that can be changed inside the calling method.
•  Variables passed to out can be passed to a function without being initialized, while ref specifies that the value is a reference value that can be changed inside the calling method.
•  Variables passed to ref specify that the parameter is an output parameter, while out specifies that a variable may be passed to a function without being initialized.

Official documentation: ref

Official documentation: out parameter modifier

Q6. How could you retrieve information about a class, as well as create an instance at runtime?

•  reflection
•  serialization
•  abstraction
•  dependency injection

Official documentation: Reflection

Q7. What is this code an example of?

    private static object objA;
    private static object objB;

    private static void performTaskA()
    {
        lock (objB)
        {
            Thread.Sleep(1000);
            lock (objA) { }
        }
    }

    private static void PerformTaskB()
    {
        lock (objA)
        {
            lock (objB) { }
        }
    }

•  a private class that uses multithreading
•  multithread coding
•  thread mismanagement
•  a potential deadlock

Official documentation: Deadlocks and race conditions

Q8. What is the difference between an anonymous type and a regular data type?

•  Anonymous types don't have type names
•  Anonymous types can only be static
•  Anonymous types can be used only in struts
•  Anonymous types don't work with LINQ.

Official documentation: Anonymous Types

Q9. When would you use a Dictionary rather that an Array type in your application?

•  when you need a jagged collection structure
•  when you need to store values of the same type
•  when you need to store key-value pairs rather than single values
•  when you need an ordered, searchable list

Official documentation: Dictionary<TKey,TValue> Class

Q10. What is the difference between a.Equals(b) and a == b?

•  The .Equals method compares reference identities while the == compares contents.
•  The .Equals method compares primitive values while == compares all values.
•  The .Equals method compares contents while == compares references reference identity.
•  The .Equals method compares reference type while == compares primitive value types.

Q11. Which choice best describes a deadlock situation?

•  when you try to instantiate two objects at the same time in the same class or struct
•  when you are trying to execute an action after a user event is registered
•  when simultaneous instructions are waiting on each other to finish before executing
•  when you try to execute a series of events simultaneously on multiple threads

Official documentation: Deadlocks and race conditions

Q12. How does the async keyword work?

•  It allows access to asynchronous methods in the C# API
•  It allows thread pooling and synchronous processes in static classes.
•  It allows the await keyword to be used in a method
•  It allows access to synchronous methods in the C# API

Official documentation: async

Q13. What is an object in C#?

•  a class or struct, including its variables and functions
•  a primitive data type that can be created only at compile time
•  a value type that can be used only with an abstract class
•  an instance of a class or struct that includes fields, properties, and/or methods

Official documentation: Objects

Q14. Which code snippet declares an anonymous type named userData?

•  var<<!---->T> userData = new <<!---->T> { name = "John", age = 32 };
•  var userData = new { name = "John", age = 32 };
•  AType userData = new AType { name = "John", age = 32 };
•  Anonymous<T> userData = new Anonymous<T> { name = "John", age = 32 };

Official documentation: Anonymous Types

Q15. What will be returned when this method is executed?

public void userInput(string charParamters) { }

•  nothing
•  a Boolean
•  a string variable
•  an integer

Official documentation: void

Q16. In what order would the employee names in this example be printed to the console?

string[] employees = { "Joe", "Bob", "Carol", "Alice", "Will" };

IEnumerable<string> employeeQuery = from person in employees
                                    orderby person
                                    select person;

foreach(string employee in employeeQuery)
{
    Console.WriteLine(employee);
}

•  ascending
•  unordered
•  descending
•  first in, first out

dotnetpattern: LINQ OrderBy Operator

Q17. Lambda expressions are often used in tandem with which of the following?

•  Namespaces
•  LINQ
•  Type Aliasing
•  Assemblies

Official documentation: Language Integrated Query (LINQ) Overview

Q18. What is the correct formatting for single line and multiline comments?

•  // - Single Line / - Multiline
•  // Multiline /_ Single Line _/
•  //* Multiline / Single Line
•  // Single Line /_ Multiline _/

w3schools: C# Comments

Q19. How do you make a method in an abstract class overridable?

•  Make it public
•  Make it static
•  Make it private
•  Make it virtual

Official documentation: virtual

Official documentation: abstract

Q20. How would you write code for an integer property called Age with a getter and setter?

•  public int Age { get - set }
•  public int Age: get set;
•  public int Age (get, set );
•  public int Age { get; set; }

Official documentation: Using Properties

Q21. What is an abstract class?

•  a class that is denoted by the class keyword (can be seen and used by any other class in the system--thus it is by default public)
•  something denoted by the abstract keyword and used system wide; if you want any program to create an object of a class you use the abstract class
•  a class that is denoted by the virtual keyword
•  a class that can be used only as base class

Official documentation: Abstract and Sealed Classes and Class Members

Q22. When using a thread pool what happens to a given thread after it finishes its task?

•  The thread is destroyed and memory is freed up.
•  The thread runs in loop until the next assignment.
•  The thread goes inactive in the background and waits for garbage collection.
•  The thread returns to the pool for reuse.

Official documentation: Thread pool characteristics

Q23. Which choice represents a class that inherits behavior from a base class?

•  a second base class
•  a revised class
•  a derived class
•  a parent class

Official documentation: Inheritance

Q24. What does operator overloading allow you to do?

•  hide built-in operatores when necessary
•  add methods to be interpreted by the compiler at runtime
•  define how enums and other primitive value types work within the rest of the application
•  define custom functionality for common operators like addition and equality

Official documentation: Operator overloading

Q25. What it the main purpose of LINQ?

•  to delete duplicate data
•  to bind namespaces and assemblies
•  to query and transform data
•  to connect assemblies

Official documentation: Language Integrated Query (LINQ) Overview

Q26. What is the correct syntax for a new generic list of strings named contacts?

•  public List contacts = new List();
•  public List(string names) contacts = new List(string names)();
•  var contacts = new List();
•  var contacts = new List(string);

Official documentation: List Class

Q27. What is the difference between throw exceptions and throw clauses?

•  Throw clauses fire only at runtime, while throw exceptions can fire at any time.
•  Throw exceptions overwrite the stack trace, while throw clauses retain the stack information.
•  Throw clauses overwrite the stack trace, while throw exceptions retain the stack information.
•  Throw exceptions fire only at runtime, while throw clauses can fire during compile time.

Official documentation: throw

c-sharpcorner: Difference Between Throw Exception and Throw Clause

Q28. When an asynchronous method is executed, the code runs but nothing happens other than a compiler warning. What is most likely causing the method to not return anything?

•  The return yield statement is missing at the end of the method.
•  The method is missing an await keyword in its body.
•  The wait keyword is missing from the end of the method.
•  The yield keyword is missing from the method.

Q29. What are C# events?

•  system actions that communicate directly with the compiler at runtime
•  actions that execute when the code compiles, generating logs and test output
•  actions that generate notifications, which are sent to their registered listeners
•  user-only methods that send data to the application's back end

Official documentation: Introduction to events

Q30. What kind of values can arrays store?

•  unordered collections of numerc values
•  key-value pairs of any C# supported type
•  class and struct instances
•  multiple variables, or collections, of the same type

Official documentation: Arrays

Q31. Given this enumeration, how would you access the integer-type value of 'AppState.Loading'?

enum AppState { OffLine, Loading, Ready }

•  string currentState = (string)AppState.Loading;
•  string currentState = AppState.Loading.integralVal;
•  int currentState = AppState.Loading.rawValue;
•  int currentState = (int)AppState.Loading;

Official documentation: Enumeration types

Q32. What character would you use to start a regular expression pattern at a word boundary?

•  d
•  \a
•  \b
•  \w

regular-expressions: Word Boundaries

Official documentation: Regular Expression Language - Quick Reference

Q33. To conform to the following interface, which of its members need to be implemented?

public interface INameble
{
    string FirstName { get; set; }
    string LastName { get; }
}

•  Both the FirstName and LastName properties need to be implemented.
•  Neither, they are both optional.
•  Only the LastName property needs to be implemented.
•  Only the FirstName property needs to be implemented.

Official documentation: interface

Q34. You're dealing with multiple assemblies in your program, but are worried about memory allocation. At what point in the program life cycle are assemblies loaded into memory?

•  at runtime
•  at compile time
•  only when required
•  only when programmatically loaded

Q35. What is most accurate description of a regular expression?

•  A regular expression is a C# tool used to parse HTML
•  A regular expression is a special text string for describing a search patters.
•  A regular expression allows a variable to be passed by reference.
•  A regular expression allows a class to conform to the Equatable protocol.

Official documentation: Regular Expression Language - Quick Reference

Official documentation: .NET regular expressions

Q36. Why would you use a class field in C#

•  To define behaviours of the class
•  To hold information and data contained in the class object
•  To communicate between classes and object
•  To store the class definition value

Official documentation: Introduction to classes

Q37. When would you use generics in your code?

•  to increase code performance
•  all of these answers
•  when code reuse is a priority
•  when type safety is important

Official documentation: Generic classes and methods

Q38. What prints to the console when this code is executed?

public delegate void AuthCallback(bool validUser);
public static AuthCallback loginCallback = Login;
public static void Login()
{
    Console.WriteLine("Valid user!");
}

public static void Main(string[] args)
{
    loginCallback(true);
}

•  Login successful...
•  Valid user!
•  an error, because the method signature of Login doesn't match the delegate
•  Login successful... Valid user!

Official documentation: Introduction to Delegates

Official documentation: Introduction to Events

Q39. How would you declare a sealed class named User?

•  public class User
•  abstract User {}
•  sealed class User
•  private sealed class User

Official documentation: Abstract and Sealed Classes and Class Members

Q40. What is the correct syntax for a new generic list of strings named contacts? (similar to Q26)

•  var contacts = new List<string>();
•  var contacts = new List(string);
•  public List<string names> contacts = new List<string names>();
•  public List(string names) contacts = new List(string names);

Official documentation: List

Q41. What is the difference between non-static and static classes?

•  non-static classes need to be initialized before use, while static classes do not
•  non-static classes are accessible only from an interface while static classes are accessible from anywhere
•  non-static classes need to initialize all class members at runtime, while static classes do not
•  non-static classes do not need to be initialized while static classes do

stackoverflow

Official documentation: Static Constructors

Q42. Which characteristic prevents this code from compiling?

public int age="28"

•  type safety
•  single inheritance
•  dependency injection
•  multiple inheritance

c-sharpcorner: Type Safety in .NET

Q43. How would you serialize this class?

public class User {}

•  Mark the User class with the DeserializableAttribute.
•  Declare the class as public serializable class User {}.
•  Mark the User class with the SerializableAttribute attribute.
•  Declare the class as private serializable class User {}.

Official documentation: SerializableAttribute Class

Q44. How would you write a delegate named ResultCallback with an int parameter named responseCode

•  public delegate ResultCallback(int responseCode)
•  public delegate void ResultCallback<(int) responseCode>;
•  public void delegate ResultCallback;
•  public delegate void ResultCallback(int responseCode);

Official documentation: Delegates

Q45. What is the difference between a static and non-static method?

•  non-static methods always need to have a void return type
•  non-static methods do not have access to static member variables
•  static methods do not have to instantiate an instance of the class to call the method
•  static methods always have to be public

Official documentation: Static Members

Q46. What is the correct way to write an event named apiResult based on a delegate named ResultCallback?

•  public void event ResultCallback apiResult;
•  public event ResultCallback(() -> apiResult);
•  public event void ResultCallback
•  public event ResultCallback apiResult;

Official documentation: Introduction to events

Q47. When will the code inside finally block be executed in a try-catch statement?

•  if there is an error, it won't execute at all
•  between the try and catch blocks
•  after the try and catch blocks
•  when the finally block overrides the catch block and executes in its place

Official documentation: try-catch

Q48. What method correctly extends the string class?

•  public static string IsvalidName(this string i, string value) {}
•  public static void IsvalidName(this string i, string value) {}
•  public string IsvalidName(this string i, string value) {}
•  public void IsvalidName(this string i, string value) {}

Q49. How are C# classses limited?

•  They do not support multiple inheritance.
•  They support multiple inheritance.
•  They can have only a set number of properties.
•  They can have only a set number of methods.

Official documentation: Class inheritance

Q50. What function do namespaces perform?

•  Namespaces calculate code coverage at runtime.
•  Namespaces compile application code together at compile time.
•  Namespaces group code together into a single repository.
•  Namespaces separate code into groupings, control access, and void naming collisions.

Official documentation: namespace

Q51. What is the correct way to write a public property with a private backing field?

• [ ]

private int _password;
pubic int Password = { get; set; }

• [ ]

private int _password;
public int Password = _password;

• [ ]

private int _password;
public int Password
{
  get -> _password;
  set-> _password = value;
}

• [x]

private int _password;
public int Password
{
  get { return _password; }
  set { _password = value; }
}

Official documentation: Using Properties

Q52. What is a thread pool?

•  a collection of synchronous methods created during initialization that cannot be reused
•  a collection of threads created during initialization that can be reused
•  a collection of threads only recognized at compile time that can be reused
•  a collection of asynchronous methods created at compile time that cannot be reused

Official documentation: ThreadPool Class

Q53. What is the most accurate description of a regular expression?

•  A regular expressions allows a variable to be passed by reference
•  A regular expression allows a class to conform to the Equatable protocol
•  A regular expression is a C# tool used to parse HTML
•  A regular expression is a special text string for describing a search pattern

Official documentation: Regular Expression Language - Quick Reference

Q54. When an object in C# is serialized, what is it converted to?

•  XML
•  JSON
•  byte stream
•  value stream

Official documentation: Serialization

Q55. What is a delegate

•  a variable that holds a reference to a value type and its content
•  a specific value type that can be used only in callback methods
•  a type that holds a reference to a method with a particular parameter list and return type
•  a custom variable type that can be used in abstract classes

Official documentation: Delegates

Q56. What are the four keywords associated with exception handling in C#?

•  try, catch, valid, invalid
•  try, valid, finally, throw
•  try, catch, finally, throw
•  finally, throw, valid, invalid

Tutorial Point

Q57. What is the main difference between the is and as operators?

•  The is operator checks instance types, while the as operator checks the inherited type.
•  The is operator checks primitive data types, while the as operator checks the object type.
•  The as operator checks object type, while the is operator attempts to cast an object to a specific type.
•  The is operator checks object type, while the as operator attempts to cast an object to a specific type.

Pluralsight guide

Q58. What is the difference between finally and finalize blocks?

•  The finally block is called during the execution of a try and catch block, while the finalize method is called after garbage collection.
•  The finally block is called after the execution of a try and catch block, while the finalize method is called just before garbage collection.
•  The finalize block is called before the execution of a try and catch block, while the finally method is called just before garbage collection.
•  The finalize block is called during the execution of a try and catch block, while the finally method is called after garbage collection.

C-sharpcorner

Q59. Your application has a value type called username that needs to be able to accept null values, but this is generating compile-time errors. How would you fix this in code?

•  Null username = null;
•  string? username = null;
•  Type? username = null;
•  Optional username = null;

Q60. Which code snippet correctly declares a custom exception named InvalidResponse?

•  struct InvalidResponse: Exception {}
•  class InvalidResponse: Exception {}
•  public Exception InvalidResponse = new Exception ();
•  public Exception InvalidResponse () -> Exception;

Official documentation: Exceptions

Q61. How would you write an enum variable called AppState with values for Offline, Loading, and Ready?

•  enum AppState = [Offline, Loading, Ready]
•  enum AppState {"Offline", "Loading", "Ready"}
•  enum AppState = {Offline, Loading, Ready}
•  enum AppState {Offline, Loading, Ready}