Junior C# Interview Questions

A nullable type allows a value type to also store a null value. It is useful when a variable may or may not have a valid data value.

First: An array has a fixed size.
Second: A List can grow or shrink dynamically.
Arrays are faster for fixed collections, Lists are flexible and easier to use.

An enum is a special value type that represents a set of named constant values.

It improves readability when working with predefined options, categories, or states.

Properties provide controlled access to internal fields of a class.

They allow getting or setting values while applying validation or logic if needed.

An indexer allows an object to be accessed like an array.

It enables retrieving values using an index without exposing internal data structures.

A delegate is a type that holds a reference to a method.

It enables methods to be treated as objects and passed as parameters.

An event allows an object to notify other objects when something happens.

Events follow the publisher–subscriber pattern and are based on delegates.

break: Immediately exits the loop.

continue: Skips the current iteration and moves to the next one.

ref: The variable must be initialized before passing.

out: Initialization is not required before passing, but must be assigned inside the method.

A sealed class cannot be inherited.

It is used to prevent further extension of a class.

A partial class allows a class definition to be split across multiple files.

Commonly used in large projects and generated code.

The using statement ensures that disposable resources are released automatically when the block ends.

A thread is the smallest unit of execution.

It allows multiple tasks to run concurrently.

Multithreading enables a program to perform multiple operations simultaneously using multiple threads.

The lock keyword prevents multiple threads from accessing a shared resource at the same time.

It ensures thread safety.

JIT compiler converts IL code into machine code at runtime.

It optimizes execution for the system's hardware and OS.

is: Checks whether an object is of a specific type.

as: Attempts conversion and returns null if conversion fails.

The base keyword is used in a derived class to access members of the parent class.

It is useful for calling parent constructors or overridden methods.

A readonly struct ensures that all fields remain immutable.

It improves performance by avoiding unnecessary copies.

Field: Stores data directly inside a class.

Property: Provides controlled access to data using getters and setters.

An anonymous type is an object created without defining a class.

The compiler generates a temporary type with read-only properties.

IEnumerable: Represents a collection that can be iterated.

IEnumerator: Performs step-by-step iteration over the collection.

IEnumerable: Executes queries in memory (LINQ to Objects).

IQueryable: Builds expression trees and allows external systems like databases to execute queries.

Extension methods allow adding new functionality to existing types without modifying their source code or creating derived classes.

A static class cannot be instantiated.

It contains only static members and is commonly used for utility functions.

The root class for all .NET types is System.Object.

It provides behaviors like equality, hashing, and type information.

A destructor is a method called when an object is being cleaned up.

It is rarely used because memory is managed by the garbage collector.

Method hiding occurs when a derived class defines a method with the same name as the parent class but does not override it.

The new method hides the parent method when accessed via the derived type.

Early binding: Type information is known at compile time.

Late binding: Type information is resolved at runtime.

The yield keyword simplifies iterator creation.

It returns values one at a time without creating a separate collection.

A generic type allows a class or method to work with multiple data types while maintaining type safety and performance.

Covariance: Allows using a more derived type than originally specified.

Contravariance: Allows using a more base type than originally specified.

Dependency Injection (DI) provides required objects from outside rather than creating them internally.

It improves modularity, testability, and maintainability.

Thread: A physical execution unit.

Task: A higher-level abstraction optimized for asynchronous operations.

async marks a method as asynchronous.

await pauses execution until the awaited task completes without blocking the thread.

A race condition happens when multiple threads access or modify shared data simultaneously, causing unpredictable behavior.

Deadlock occurs when multiple threads wait for each other's resources and none of them can continue.

Stack: Stores value types and method call information.

Heap: Stores reference types and dynamically allocated objects.

An attribute is metadata applied to program elements like classes, methods, or properties.

It helps frameworks control behavior at compile time or runtime.