10 C# Interview Questions and Answers in 2023
1. Describe the differences between value types and reference types in C#.
Value types in C# are stored on the stack and are allocated memory when declared. They are immutable, meaning they cannot be changed once they are created. Examples of value types include int, float, char, and bool.
Reference types in C# are stored on the heap and are allocated memory when they are instantiated. They are mutable, meaning they can be changed after they are created. Examples of reference types include classes, strings, and objects.
The main difference between value types and reference types is that value types are stored directly in memory, while reference types are stored as a reference to the memory location where the object is stored. This means that when a value type is passed to a method, a copy of the value is created and passed to the method, while when a reference type is passed to a method, a reference to the object is passed instead.
2. Explain the concept of inheritance in C# and how it is used.
Inheritance is a fundamental concept in object-oriented programming (OOP) languages such as C#. It is a way of creating a new class (called a derived class) from an existing class (called a base class). The derived class inherits all the members of the base class, including fields, methods, and properties. This allows the derived class to reuse the code of the base class, while also adding its own unique features.
Inheritance is used to create a hierarchical relationship between classes. This allows for code reuse and simplifies the development process. For example, if you have a base class called Animal, you can create derived classes such as Dog, Cat, and Horse. These derived classes will inherit all the members of the Animal class, but can also add their own unique features.
Inheritance is also used to create polymorphism, which is the ability of an object to take on different forms. For example, if you have a base class called Shape, you can create derived classes such as Circle, Square, and Triangle. These derived classes will all inherit the members of the Shape class, but can also override the methods of the base class to create their own unique behavior.
In C#, inheritance is implemented using the keyword “:”. For example, if you wanted to create a derived class called Dog from the base class Animal, you would write the following code:
public class Dog : Animal
{
// Dog-specific code
}
In summary, inheritance is a fundamental concept in C# and other OOP languages. It allows for code reuse and simplifies the development process by creating a hierarchical relationship between classes. It also allows for polymorphism, which is the ability of an object to take on different forms.
3. What is the purpose of the using statement in C#?
The using statement in C# is a directive that allows the programmer to include a library or namespace in their code without having to fully qualify the names of the types within that library or namespace. This is especially useful when dealing with large libraries or namespaces that contain many types. By using the using statement, the programmer can avoid having to type out the full name of each type they wish to use, which can save time and make the code more readable. Additionally, the using statement can be used to create aliases for types, which can also help to make the code more readable.
4. How do you handle exceptions in C#?
Exceptions in C# are handled using the try-catch-finally block. The try block contains the code that may throw an exception. The catch block contains the code that will handle the exception. The finally block contains the code that will always be executed, regardless of whether an exception is thrown or not.
To handle an exception, the code in the try block is executed. If an exception is thrown, the code in the catch block is executed. The catch block can contain multiple catch blocks, each with a different exception type. This allows for different types of exceptions to be handled differently.
Once the code in the catch block has been executed, the code in the finally block is executed. This allows for any clean-up code to be executed, regardless of whether an exception was thrown or not.
In addition to the try-catch-finally block, C# also provides the using statement. The using statement allows for the automatic disposal of objects, such as database connections, when the code exits the using block. This ensures that any resources used by the object are released when the code exits the using block.
5. What is the difference between a struct and a class in C#?
The primary difference between a struct and a class in C# is that a struct is a value type and a class is a reference type.
A struct is a lightweight alternative to a class and is used to store small amounts of data. Structs are stored on the stack, which means that they are allocated and deallocated very quickly. Structs are also immutable, meaning that their values cannot be changed once they are created.
A class, on the other hand, is a reference type and is used to store more complex data. Classes are stored on the heap, which means that they take longer to allocate and deallocate. Classes are also mutable, meaning that their values can be changed after they are created.
In addition, structs cannot have explicit parameterless constructors, whereas classes can. Structs also cannot inherit from other structs or classes, whereas classes can. Finally, structs cannot have destructors, whereas classes can.
6. Describe the process of creating a custom attribute in C#.
Creating a custom attribute in C# is a relatively straightforward process.
First, you need to create a class that derives from the Attribute class. This class should contain any properties that you want to be associated with the attribute. For example, if you wanted to create an attribute that specified the author of a piece of code, you would create a class with a property called Author.
Next, you need to decorate the class with the AttributeUsage attribute. This attribute allows you to specify the types of elements that the attribute can be applied to, such as classes, methods, or properties.
Once the attribute class is created, you can apply it to any element that you specified in the AttributeUsage attribute. For example, if you wanted to apply the Author attribute to a class, you would use the following syntax:
[Author("John Doe")]
public class MyClass
{
// ...
}
Finally, you can access the attribute from code by using the GetCustomAttribute method. This method takes the type of the attribute as a parameter and returns an instance of the attribute. You can then access the properties of the attribute to get the values that were specified when the attribute was applied.
For example, if you wanted to get the author of a class, you could use the following code:
var authorAttribute = (AuthorAttribute)Attribute.GetCustomAttribute(typeof(MyClass), typeof(AuthorAttribute));
string author = authorAttribute.Author;
7. What is the purpose of the lock keyword in C#?
The lock keyword in C# is used to ensure that only one thread can access a particular resource at a given time. This is known as mutual exclusion, and it is used to prevent race conditions and deadlocks. The lock keyword is used to create a block of code that can only be accessed by one thread at a time. This is done by using the System.Threading.Monitor class to acquire a lock on a particular object. Once the lock is acquired, any other threads that attempt to access the same object will be blocked until the lock is released. This ensures that only one thread can access the object at a time, and that any changes made to the object are done in a thread-safe manner.
8. Explain the concept of generics in C# and how they are used.
Generics in C# are a way of creating classes and methods that can work with any data type. This allows developers to create code that is more flexible and reusable. Generics are used to create classes and methods that can work with any data type, without having to write separate code for each data type.
Generics are declared using angle brackets (<>) and the type parameter. For example, a generic List class might be declared like this:
List
The type parameter T is used to represent any data type. When the List class is used, the type parameter is replaced with a specific data type. For example, a List of strings might be declared like this:
List
Generics can also be used to create methods that can work with any data type. For example, a generic method to find the maximum value in an array might be declared like this:
public static T Max
The type parameter T is used to represent any data type. When the method is used, the type parameter is replaced with a specific data type. For example, a method to find the maximum value in an array of integers might be declared like this:
public static int Max(int[] array)
Generics are a powerful tool for creating code that is more flexible and reusable. They allow developers to create classes and methods that can work with any data type, without having to write separate code for each data type.
9. Describe the differences between a delegate and an event in C#.
A delegate in C# is a type that defines a method signature. It is a reference type that can be used to encapsulate a named or an anonymous method. Delegates are used to pass methods as arguments to other methods, to define callback methods and to implement events and event handlers.
An event in C# is a way for a class to provide notifications to clients of that class when some interesting thing happens to an object. Events are based on delegates. When an event is raised, the delegate associated with the event is invoked. Events are declared using the event keyword and follow the same rules as fields.
In summary, a delegate is a type that defines a method signature, while an event is a way for a class to provide notifications to clients of that class when some interesting thing happens to an object. Events are based on delegates and are declared using the event keyword.
10. How do you create a thread in C# and what are the benefits of using threads?
Creating a thread in C# is a relatively straightforward process. To create a thread, you must first create a new instance of the System.Threading.Thread class. You can then pass a delegate to the Thread constructor, which will be used to execute the code that will run on the thread.
The benefits of using threads are numerous. Threads allow for concurrent execution of code, meaning that multiple tasks can be executed at the same time. This can lead to improved performance, as tasks can be executed in parallel instead of sequentially. Threads also allow for better resource utilization, as multiple tasks can be executed on the same processor. Finally, threads can be used to improve the responsiveness of an application, as tasks can be executed in the background while the user interacts with the application.