Preparing for a C# interview requires more than rote learning the answers. You must have a deep understanding of the language and know how to use it practically. So, take the time to go over 100 C# technical interview questions before going to your next interview. Interviewers are impressed by candidates who come prepared and can speak about C# fundamentals and show a real-world application of concepts. By going through the following questions, you will be able to strengthen your knowledge and answer questions the right way. Whether you wish to apply for an entry-level role or a senior position, being well-prepared can set you apart from other candidates. Use this interview questions guide to brush up on your skills and ace your C# interview.
Answer: Circular references occur when two or more resources depend on each other, resulting in a deadlock condition where the resources become unusable.
Answer: Generics in C# allow you to defer specifying the data type of programming elements in a class or method until they are used in the program. This means that you can write a class or method that can work with any data type. Key features of Generics include:
- Generics are a technique that enhances the programs in the following ways:
- It helps to maximize code reuse, type safety, and performance.
- Allows creation of generic collection classes. The .NET Framework class library contains numerous new generic collection classes in the System.Collections.Generic namespace. You should use these generic collection classes in place of the collection classes in the System.Collections namespace.
- You can make your own generic classes, methods, interfaces, events, and delegates.
- You may create generic classes constrained to allow access to methods on specific data types.
- You may get information on the types useful in a generic data type at run-time using reflection.
Answer: In .NET, an object pool is a container that holds pre-created objects, ready to be used. It helps in tracking the availability of objects and the total number of objects in the pool. By using an object pool, the need for frequent object creation and disposal is reduced, leading to improved performance.
Answer: Commonly used types of exceptions in .NET include:
- ArgumentException
- ArithmeticException
- DivideByZeroException
- OverflowException
- InvalidCastException
- InvalidOperationException
- NullReferenceException
- OutOfMemoryException
- StackOverflowException
Answer: Custom exceptions are exceptions that are specifically created to handle errors according to specific user requirements or application-specific scenarios. These exceptions allow developers to define their own exception types to handle exceptional situations in a customized manner.
Answer: Delegates in C# are similar to function pointers in C++. They provide a way to refer to methods and pass them as parameters, allowing for the creation of type-safe and generic functions. Delegates enable the encapsulation of method references, making them highly useful for event handling and callback mechanisms.
Answer: Method overriding involves replacing the implementation of a method in the derived class, thereby changing its behavior. On the other hand, method overloading refers to creating multiple methods with the same name within the same class, but with different signatures (parameter types, number, or order). Overloading allows for multiple methods with similar functionality but different ways of accepting or returning values.
Answer: In C#, class inheritance is accomplished using the inheritance operator, which is a colon (:). To inherit one class into another, you specify the derived class name, followed by a colon and the base class name.
Answer: In C#, a method can be overloaded in multiple ways: Using different data types for a parameter. Changing the order of parameters. Varying the number of parameters.
Answer: In an interface, all methods are implicitly virtual and intended to be overridden in the derived classes. Therefore, they are inherently public and cannot have their accessibility explicitly specified. The purpose of an interface is to define a contract that derived classes must follow, and the accessibility of the methods is automatically determined by the implementing classes.
Answer: Here are some common differences between an interface and an abstract class in C#. A class is capable of implementing any number of interfaces, but a subclass can, at the most, use only one abstract class. An abstract class can have non-abstract methods (concrete methods), however, in the case of interface, all the methods should be abstract. An abstract class can declare or use any variables, but an interface cannot do so. In an abstract class, data members or functions are by default private, while in an interface, all are public; you can’t change them manually. In an abstract class, you need to use abstract keywords to declare abstract methods; in an interface, we don’t need that. An abstract class can not be utilized for multiple inheritance, whereas the interface can be used for multiple inheritance. An abstract class utilizes a constructor, while we don’t have any constructor in an interface.
Answer: In C#, the “enum” keyword is used to define an enumerated type, which represents a collection of related constants known as an enumerated list. Enums can be of various types, such as int, float, double, or byte. Explicit casting is necessary if the enum is not of type int. Using the .NET framework enum, it is possible to create numeric constants. Int is the default of the enumeration element. By default, the first enumerator has the value 0, and each subsequent enumerator is incremented by 1, similar to an array.
Answer: The “this” keyword cannot be used in a static method because it refers to the current instance of the class containing it. Static methods, including all static members, do not belong to a specific instance. They exist without the need for creating an instance of the class and are invoked using the class name. Therefore, the “this” keyword cannot be used within the body of static methods. However, in the case of Extension Methods, it is possible to use parameters of the method to achieve similar functionality.
Answer: Properties in C# are class members that provide a way to read, write, or compute the value of a private field. They expose a public interface to access and modify the data stored in a class while allowing the class to control how that data is accessed and manipulated. Properties are declared using get and set accessors, which define the behavior for retrieving or assigning the property value. The get accessor retrieves the property’s value, while the set accessor sets the property’s value. A property can have one or both accessors, depending on whether it is read-only, write-only, or read-write.
Answer: In C#, an extension method is a static method used to extend the functionality of an existing type without modifying the original type or creating a new derived type. Extension methods enable developers to add methods to existing types such as classes, structs, interfaces, enums, etc., even if those types were not initially designed to include those methods. Extension methods are declared within a static class and defined as static methods. They have a special first parameter called the “this” parameter, which specifies the type being extended. This allows the extension method to be invoked as if it were an instance method of that type.
Answer: A Data Transfer Object (commonly identified as a DTO) is an instance of a POCO (plain old CLR object) class used as a container to encapsulate and transport data between different layers or components of an application. DTOs is used commonly in the service layer (backend) to return data back to the presentation layer (frontend).
Answer: StringBuilder and string are used to string values, but both have distinct differences in terms of instance creation and performance.
- String objects are immutable that holds a string value whereas StringBuilder is a mutable object.
- Performance-wise, a string is slower as it creates a new instance to override or change the previous value as compared to StringBuilder which faster because it uses the same instance of the StringBuilder object to perform any operation, like inserting a value in the existing string.
- String belongs to the System namespace while StringBuilder belongs to System.Text namespace.
Answer: Delegates in C# enable methods to be passed as parameters, allowing for greater flexibility and code reusability. Delegates can be used to define callback methods and facilitate event handling. Multiple methods can be combined or assigned to a single delegate, enabling invocation of multiple methods with a single call. The delegate type does not have to match the exact signature of the methods it references, providing a level of abstraction and flexibility.
Answer: Sealed classes in C# are used to restrict inheritance, preventing other classes from deriving from them. Once a class is defined as sealed, it cannot be used as a base class for other classes. Sealed classes are commonly employed when the behavior and implementation of a class are considered complete and should not be extended or modified further. In C#, the sealed modifier is applied to a class definition to declare it as sealed. In Visual Basic .NET, the NotInheritable keyword serves the same purpose. If a class is derived from a sealed class, the compiler generates an error. It’s worth noting that structs, by default, are also sealed.
Answer: IEnumerable interface in C# defines one method, GetEnumerator which returns an IEnumerator interface. This lets readonly access to a collection then a collection that implements IEnumerable can be utilized with a for-each statement. Key Points
- IEnumerable interface comprises the System.Collections.Generic namespace.
- IEnumerable interface is a generic interface which permits looping over generic or non-generic lists.
- IEnumerable interface works with linq query expression.
- IEnumerable interface Returns an enumerator that iterates through the collection.