- 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.
- 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
- reactive
- inherited callback
- task-based
- callback-based
Official documentation: Task asynchronous programming model
- .
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
- 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: out parameter modifier
- reflection
- serialization
- abstraction
- dependency injection
Official documentation: Reflection
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
- 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
- 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
- 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.
- 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
- 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
- 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
-
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
public void userInput(string charParamters) { }
- nothing
- a Boolean
- a string variable
- an integer
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
- Namespaces
- LINQ
- Type Aliasing
- Assemblies
Official documentation: Language Integrated Query (LINQ) Overview
- // - Single Line / - Multiline
- // Multiline /_ Single Line _/
- //* Multiline / Single Line
- // Single Line /_ Multiline _/
- Make it public
- Make it static
- Make it private
- Make it virtual
Official documentation: virtual
Official documentation: abstract
- public int Age { get - set }
- public int Age: get set;
- public int Age (get, set );
- public int Age { get; set; }
Official documentation: Using Properties
- 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
- 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
- a second base class
- a revised class
- a derived class
- a parent class
Official documentation: Inheritance
- 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
- to delete duplicate data
- to bind namespaces and assemblies
- to query and transform data
- to connect assemblies
Official documentation: Language Integrated Query (LINQ) Overview
- 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
- 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.
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.
- 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
- 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
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
- d
- \a
- \b
- \w
regular-expressions: Word Boundaries
Official documentation: Regular Expression Language - Quick Reference
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
- 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
- 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
- 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
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
- public class User {}
- abstract User {}
- sealed class User {}
- private sealed class User {}
Official documentation: Abstract and Sealed Classes and Class Members
-
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);
- 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
Official documentation: Static Constructors
public int age="28"
- type safety
- single inheritance
- dependency injection
- multiple inheritance
c-sharpcorner: Type Safety in .NET
public class User {}
- Mark the User class with the
DeserializableAttribute. - Declare the class as
public serializable class User {}. - Mark the User class with the
SerializableAttributeattribute. - Declare the class as
private serializable class User {}.
Official documentation: SerializableAttribute Class
- public delegate ResultCallback(int responseCode);
- public delegate void ResultCallback<(int) responseCode>;
- public void delegate ResultCallback<int responseCode>;
- public delegate void ResultCallback(int responseCode);
Official documentation: Delegates
- 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
- 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
- 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) {}
- 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
- 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
- [ ]
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
- 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
- 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
- XML
- JSON
- byte stream
- value stream
Official documentation: Serialization
- 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
- try, catch, valid, invalid
- try, valid, finally, throw
- try, catch, finally, throw
- finally, throw, valid, invalid
- 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.
- 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.
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;
- 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}
- A value type can be any primitive type, while reference types must be type-agnostic.
- A value type refers to another value, while a reference type refers to a value in memory.
- A value type stores an actual value, while a reference type is a pointer to a value.
- A value type is available only at runtime, while a reference type is available only at compile time.
Official documentation: Value types
Official documentation: Reference types
- The
breakkeyword is used to break out of multiple iteration statements, whilecontinuecan only break out of code blocks that have single iterations. - The
breakkeyword literally breaks out of a control flow statement, whilecontinueignores the rest of the control statement or iteration and starts the next one. - The
breakkeyword literally breaks out of the current control flow code and stops it dead, whilecontinuekeeps executing the code after an exception is thrown. - The
breakkeyword jumps out of an iteration and then proceeds with the rest of the control flow code, whilecontinuestops the executing code dead.
Official documentation: Jump statements
Q64. Which code snippet correctly declares a variable named userId with a public get and private set?
-
public int userID <get, set>; -
public int userID [get, private set]; -
public int userID { get; private set; } -
public int userID = { public get, private set };
Official documentation: Properties
-
Overriding virtual methods in a derived class is mandatory. -
Overriding virtual methods in a derived class is not possible. -
Virtual methods always need a default implementation. -
Virtual methods cannot have default implementation.
Official documentation: virtual
c-sharpcorner: Virtual Method in C#
Q66. What is likely to happen if you have multiple threads accessing the same resource in your program?
-
resource overload -
thread jumping -
deadlock and race conditions -
nothing, since this is what threading is for
-
A string cannot be nullable. -
string? myVariable -
string myVariable = null -
string(null) myVariable
-
No, you can declare it the parameter list. -
Out variables are no longer part of C#. -
You must declare it if it is a primitive type. -
Yes.
-
People[..^2] -
You cannot do this in C#. -
People[..^3] -
People[^2]
Official Documentation: Ranges
-
at compile time -
after runtime -
at runtime -
after compile time
C-sharpcorner: Anonymous Types
-
Thread multitasking allows code to be executed concurrently -
Thread multitasking allows code to be executed only when handling a user event. -
Thread multitasking blocks code from being executed simultaneously to guard memory. -
Thread multitasking adds single-threaded code blocks together.