Here are 50 C# interview questions with answers
1. What is the difference between const, readonly, and static in C#?
English: const defines a constant value that must be assigned at compile-time and cannot be changed. readonly allows a value to be assigned either at declaration or in a constructor and can only be changed in these contexts. static applies to a member that belongs to the type itself rather than an instance.
Chinese: const定义了一个常量值，必须在编译时分配且不能更改。readonly允许值在声明时或构造函数中分配，并且只能在这些上下文中更改。static适用于属于类型本身而不是实例的成员。
2. Explain the difference between abstract class and interface in C#.
English: An abstract class can have both abstract methods (without implementation) and concrete methods (with implementation). An interface only declares methods without any implementation. Multiple interfaces can be implemented by a class, but only one abstract class can be inherited.
Chinese: abstract class可以包含抽象方法（没有实现）和具体方法（有实现）。interface仅声明没有实现的方法。类可以实现多个接口，但只能继承一个抽象类。
3. What is the purpose of the async and await keywords in C#?
English: The async and await keywords are used for asynchronous programming in C#. async is applied to a method to declare that it contains asynchronous code. await pauses the execution of the method until the awaited task completes, allowing the calling thread to continue working.
Chinese: async和await关键字用于C#中的异步编程。async应用于方法，声明该方法包含异步代码。await暂停方法的执行，直到等待的任务完成，允许调用线程继续工作。
4. How is exception handling done in C#?
English: Exception handling in C# is done using try, catch, finally, and throw blocks. The try block contains code that might throw an exception, catch handles specific exceptions, finally runs regardless of exceptions, and throw rethrows exceptions.
Chinese: C#中的异常处理使用try、catch、finally和throw块。try块包含可能抛出异常的代码，catch处理特定的异常，finally无论是否有异常都会运行，throw重新抛出异常。
5. What is the difference between Task and Thread in C#?
English: A Task represents an asynchronous operation and is part of the Task Parallel Library (TPL), optimized for concurrency. A Thread represents an independent execution path. Tasks are generally preferred because they are more lightweight and easier to manage than threads.
Chinese: Task表示一个异步操作，是任务并行库（TPL）的一部分，优化了并发。Thread表示一个独立的执行路径。Task通常更轻量级且更易于管理，因此优于线程。
6. How does garbage collection work in C#?
English: Garbage collection in C# is automatic, managed by the .NET runtime. It reclaims memory by collecting and freeing objects that are no longer in use. It works in generations (0, 1, 2), where Generation 0 is for short-lived objects, and Generation 2 is for long-lived objects.
Chinese: C#中的垃圾回收是自动的，由.NET运行时管理。它通过收集和释放不再使用的对象来回收内存。它按代（0、1、2）工作，0代用于短生命周期对象，2代用于长生命周期对象。
7. What is the difference between IEnumerable and IQueryable?
English: IEnumerable is used for in-memory collections and supports deferred execution but processes the data in memory. IQueryable is used for querying out-of-memory collections like databases and performs deferred execution with remote query evaluation, meaning the actual query is translated to SQL.
Chinese: IEnumerable用于内存中的集合，支持延迟执行，但在内存中处理数据。IQueryable用于查询内存外集合，如数据库，并执行延迟执行，实际查询转换为SQL在远程执行。
8. What is dependency injection, and why is it useful in C#?
English: Dependency injection (DI) is a design pattern where an object’s dependencies are provided by an external source rather than the object creating them itself. In C#, DI is useful because it improves testability, maintainability, and separation of concerns in applications.
Chinese: 依赖注入（DI）是一种设计模式，其中对象的依赖关系由外部来源提供，而不是对象自行创建。在C#中，DI非常有用，因为它提高了应用程序的可测试性、可维护性和关注点分离。
9. How do you prevent memory leaks in C#?
English: Memory leaks can be prevented by properly managing object references, avoiding circular references, and ensuring that IDisposable objects are properly disposed of using using statements or Dispose() method. Weak references can also be used for temporary objects.
Chinese: 可以通过正确管理对象引用、避免循环引用以及确保使用using语句或Dispose()方法正确处理IDisposable对象来防止内存泄漏。也可以使用弱引用来管理临时对象。
10. Explain the SOLID principles in C#.
English: SOLID is a set of five design principles:
- S – Single Responsibility Principle: A class should have one and only one reason to change.
- O – Open/Closed Principle: Classes should be open for extension but closed for modification.
- L – Liskov Substitution Principle: Derived classes must be substitutable for their base classes.
- I – Interface Segregation Principle: Clients should not be forced to depend on interfaces they don’t use.
- D – Dependency Inversion Principle: High-level modules should not depend on low-level modules; both should depend on abstractions.
Chinese: SOLID是五个设计原则的集合：
- S – 单一职责原则：类应该只有一个改变的理由。
- O – 开放封闭原则：类应该对扩展开放，但对修改封闭。
- L – 里氏替换原则：派生类必须可以替代基类。
- I – 接口隔离原则：客户端不应被迫依赖它们不使用的接口。
- D – 依赖倒置原则：高层模块不应依赖低层模块，二者都应依赖抽象。
11. What is LINQ, and how does it work in C#?
English: LINQ (Language-Integrated Query) allows querying collections (in-memory or out-of-memory) using a SQL-like syntax within C#. LINQ queries can operate on arrays, lists, XML, databases, and more by providing a unified way to filter, sort, group, and transform data.
Chinese: LINQ（语言集成查询）允许使用类似SQL的语法在C#中查询集合（内存或内存外）。LINQ查询可以操作数组、列表、XML、数据库等，通过提供统一的方式来过滤、排序、分组和转换数据。
12. What are extension methods in C#?
English: Extension methods allow you to "extend" existing types with new methods without modifying the original type. This is done by creating a static method in a static class, where the first parameter is the type being extended, prefixed with this.
Chinese: 扩展方法允许您通过创建静态方法为现有类型添加新方法，而无需修改原始类型。可以在静态类中创建静态方法，第一个参数是要扩展的类型，并以this作为前缀。
13. What is the difference between value types and reference types in C#?
English: Value types (like int, bool, structs) store data directly and are stored on the stack. Reference types (like class, interface, object) store references to the data on the heap. When a value type is copied, its value is copied, while a reference type copy points to the same memory address.
Chinese: 值类型（如int、bool、structs）直接存储数据，存储在栈上。引用类型（如class、interface、object）存储对堆上数据的引用。复制值类型时，复制其值；复制引用类型时，复制的是内存地址。
14. How do you implement a thread-safe singleton pattern in C#?
English: A thread-safe singleton in C# can be implemented using a static constructor, Lazy<T>, or a lock inside the instance check. The Lazy<T> approach is preferred as it ensures thread safety without the need for manual locking.
Chinese: 在C#中，线程
安全的单例模式可以使用static构造函数、Lazy<T>或在实例检查中使用lock来实现。Lazy<T>方法更为优选，因为它无需手动锁定即可确保线程安全。
15. What is covariance and contravariance in C#?
English: Covariance allows you to use a more derived type than originally specified (for return types), and contravariance allows you to use a more generic type (for parameters). Covariance and contravariance enable more flexibility in method, delegate, and interface designs.
Chinese: 协变允许您使用比原始指定的类型更派生的类型（对于返回类型），而逆变允许您使用更通用的类型（对于参数）。协变和逆变使方法、委托和接口设计更加灵活。
16. How does the yield keyword work in C#?
English: The yield keyword is used to return elements one at a time from an iterator method in C#. It allows you to lazily generate elements, only producing them when the iterator moves to the next item, which is memory-efficient for large datasets.
Chinese: yield关键字用于从C#中的迭代器方法中逐个返回元素。它允许您懒加载生成元素，仅当迭代器移动到下一个项时生成元素，这对于大型数据集非常节省内存。
17. What is reflection in C# and how is it used?
English: Reflection in C# allows you to inspect and interact with object types at runtime. Using the System.Reflection namespace, you can dynamically invoke methods, access fields and properties, and examine metadata, making it useful for frameworks and dynamic operations.
Chinese: C#中的反射允许您在运行时检查和操作对象类型。使用System.Reflection命名空间，您可以动态调用方法、访问字段和属性，并检查元数据，这对于框架和动态操作非常有用。
18. What is a delegate, and how does it work in C#?
English: A delegate in C# is a type that represents references to methods with a specific signature. It allows methods to be passed as arguments, enabling callback functionality. Delegates are often used with event handling.
Chinese: C#中的delegate是一种表示具有特定签名的方法引用的类型。它允许将方法作为参数传递，从而实现回调功能。委托通常与事件处理一起使用。
19. How do you implement event handling in C#?
English: Event handling in C# is implemented using delegates and the event keyword. A delegate defines the signature for the event handler, and the event keyword associates the delegate with the event. You can add or remove event handlers using += and -=.
Chinese: 在C#中，事件处理使用委托和event关键字实现。委托定义了事件处理程序的签名，event关键字将委托与事件相关联。您可以使用+=和-=添加或删除事件处理程序。
20. What is the difference between Func, Action, and Predicate delegates in C#?
English: Func is a delegate that returns a value and can take multiple parameters. Action does not return a value but can take multiple parameters. Predicate is a specialized Func delegate that always returns a bool and is typically used for filtering logic.
Chinese: Func是一个返回值并可以接受多个参数的委托。Action不返回值，但可以接受多个参数。Predicate是一个专门的Func委托，始终返回bool，通常用于过滤逻辑。
Certainly! Here are the remaining 30 senior-level C# interview questions and answers, continuing in the same format:
21. How do you implement exception filters in C#?
English: Exception filters in C# are implemented using the when keyword in a catch block. This allows you to catch exceptions only when a certain condition is true, making error handling more precise.
Chinese: C#中的异常过滤器使用when关键字在catch块中实现。这允许您仅在某个条件为真时捕获异常，使错误处理更加精确。
22. What is the difference between Array and List<T> in C#?
English: An Array is a fixed-size, strongly typed collection of objects, while List<T> is a dynamic-size collection that can grow or shrink. List<T> provides more methods for manipulation, such as Add(), Remove(), and Contains().
Chinese: Array是一个固定大小的强类型对象集合，而List<T>是一个可以动态增减大小的集合。List<T>提供了更多的操作方法，如Add()、Remove()和Contains()。
23. How does the lock keyword work in C#?
English: The lock keyword in C# ensures that a block of code can only be executed by one thread at a time. It prevents race conditions by providing mutual exclusion, which is important for synchronizing access to shared resources.
Chinese: C#中的lock关键字确保一段代码只能由一个线程同时执行。它通过提供互斥来防止竞态条件，这对于同步访问共享资源非常重要。
24. What is the difference between overloading and overriding in C#?
English: Overloading allows you to define multiple methods with the same name but different parameter lists within the same class. Overriding allows a subclass to provide a specific implementation of a method that is already defined in its parent class.
Chinese: 重载允许您在同一个类中定义多个具有相同名称但不同参数列表的方法。重写允许子类提供已经在其父类中定义的方法的特定实现。
25. Explain the concept of boxing and unboxing in C#.
English: Boxing is the process of converting a value type to an object or any interface type. Unboxing is the reverse, converting an object back to a value type. Boxing stores the value type on the heap, which can impact performance due to the overhead of allocating heap memory.
Chinese: 装箱是将值类型转换为object或任何接口类型的过程。拆箱则是相反的，将对象转换回值类型。装箱将值类型存储在堆上，由于分配堆内存的开销，可能会影响性能。
26. What are attributes in C#, and how are they used?
English: Attributes in C# are metadata attached to assemblies, classes, methods, properties, etc., to provide additional information about behaviors. You can define custom attributes by deriving from the System.Attribute class. Attributes are commonly used for frameworks, serialization, and validation.
Chinese: C#中的属性是附加到程序集、类、方法、属性等的元数据，用于提供有关行为的附加信息。您可以通过从System.Attribute类派生来自定义属性。属性通常用于框架、序列化和验证。
27. Explain the using statement and its purpose in C#.
English: The using statement ensures that IDisposable objects, such as file or database connections, are properly disposed of after their usage. It automatically calls the Dispose() method at the end of the block, ensuring the release of resources.
Chinese: using语句确保像文件或数据库连接这样的IDisposable对象在使用后得到正确处理。它会在块结束时自动调用Dispose()方法，以确保释放资源。
28. What are generics in C#?
English: Generics in C# allow you to define classes, methods, and delegates with a placeholder for data types. This allows type-safe operations without specifying the exact data type during implementation, promoting code reuse and reducing runtime errors.
Chinese: C#中的泛型允许您定义具有数据类型占位符的类、方法和委托。这允许在实现过程中进行类型安全的操作，而无需指定确切的数据类型，从而促进代码重用并减少运行时错误。
29. How does Null Coalescing work in C#?
English: The null coalescing operator (??) returns the left-hand operand if it is not null; otherwise, it returns the right-hand operand. This is useful for providing default values when dealing with nullable types or reference types that may be null.
Chinese: 空合并操作符（??）如果左侧操作数不为null则返回左侧操作数，否则返回右侧操作数。这在处理可空类型或可能为null的引用类型时用于提供默认值。
30. What is the difference between finalize and dispose in C#?
English: Finalize is a destructor that is called by the garbage collector before an object is reclaimed, but its exact timing is uncertain. Dispose is explicitly called to release unmanaged resources deterministically. Dispose() can be called using the IDisposable interface.
Chinese: Finalize是由垃圾回收器在回收对象之前调用的析构函数，但它的调用时间不确定。Dispose则显式调用，以确定性地释放非托管资源。可以通过IDisposable接口调用Dispose()。
31. How does async/await improve performance in C#?
English: async/await allows non-blocking asynchronous programming, where the main thread is free to perform other tasks while waiting for I/O-bound operations to complete. This improves performance by preventing thread starvation and improving resource utilization.
Chinese: async/await允许非阻塞的异步编程，主线程可以在等待I/O绑定操作完成时自由执行其他任务。这通过防止线程饥饿和提高资源利用率来改善性能。
32. What is a sealed class in C#?
English: A sealed class in C# is a class that cannot be inherited by other classes. This is useful when you want to prevent further inheritance and ensure the final implementation of a class.
Chinese: C#中的sealed类是一个不能被其他类继承的类。这在您想防止进一步继承并确保类的最终实现时非常有用。
33. What is the purpose of the volatile keyword in C#?
English: The volatile keyword is used to indicate that a field might be modified by multiple threads. It tells the compiler and runtime not to optimize the field’s access and ensures that the latest value is always read.
Chinese: volatile关键字用于指示一个字段可能被多个线程修改。它告诉编译器和运行时不要优化字段的访问，并确保始终读取最新的值。
34. What are the access modifiers in C# and their scope?
English: The access modifiers in C# include public, private, protected, internal, and protected internal. public is accessible from any code, private is accessible only within the containing class, protected is accessible within the class and derived classes, internal is accessible within the same assembly, and protected internal is accessible within the same assembly or derived classes.
Chinese: C#中的访问修饰符包括public、private、protected、internal和protected internal。public可以从任何代码访问，private只能在包含类中访问，protected可以在类和派生类中访问，internal可以在同一程序集内访问，protected internal可以在同一程序集或派生类中访问。
35. What are partial classes and methods in C#?
English: partial classes allow you to split the implementation of a class into multiple files. partial methods allow you to declare methods in one part of the class and optionally implement them in another part. This is useful in code generation scenarios.
Chinese: partial类允许您将类的实现拆分为多个文件。partial方法允许您在类的一个部分声明方法，并在另一个部分可选地实现它们。这在代码生成场景中非常有用。
36. Explain memory management in C#.
English: Memory management in C# is handled by the .NET garbage collector, which automatically reclaims memory by cleaning up objects that are no longer in use. The developer can help by explicitly disposing of resources using IDisposable and ensuring large objects or unmanaged resources are properly released.
Chinese: C#中的内存管理由.NET垃圾回收器处理，它通过清理不再使用的对象来自动回收内存。开发人员可以通过显式处理IDisposable对象和确保适当地释放大型对象或非托管资源来帮助内存管理。
37. What is LINQ to SQL in C#?
English: `LIN
Q to SQL` is a component of LINQ that provides a runtime infrastructure for managing relational data as objects. It allows you to query and manipulate SQL databases using LINQ syntax directly, providing a type-safe, object-oriented view of data.
Chinese: LINQ to SQL是LINQ的一个组件，它为以对象形式管理关系数据提供了运行时基础设施。它允许您使用LINQ语法直接查询和操作SQL数据库，提供类型安全的面向对象的数据视图。
38. How does StringBuilder work, and when should it be used?
English: StringBuilder is a class in C# that is used for efficient string manipulation when multiple modifications to a string are required. Unlike the string class, which creates a new object every time it’s modified, StringBuilder modifies the existing object, making it more performant for repetitive operations.
Chinese: StringBuilder是C#中的一个类，当需要对字符串进行多次修改时，它用于高效的字符串操作。与每次修改时都创建新对象的string类不同，StringBuilder修改现有对象，使其在重复操作中性能更高。
39. Explain how you can create and use a thread in C#.
English: Threads in C# can be created using the Thread class or by using the Task class for more advanced scenarios. The Thread class allows you to start, stop, and join threads, while Task is preferred for concurrent tasks, with better integration into the async/await model.
Chinese: 在C#中，您可以使用Thread类创建线程，或者在更高级的场景中使用Task类。Thread类允许您启动、停止和合并线程，而Task更适合并发任务，并且与async/await模型更好地集成。
40. What are asynchronous delegates in C#?
English: Asynchronous delegates allow methods to be executed asynchronously by invoking them using BeginInvoke and EndInvoke. These methods provide a mechanism for non-blocking operations, enabling better performance for I/O-bound or long-running tasks.
Chinese: 异步委托允许通过使用BeginInvoke和EndInvoke异步执行方法。这些方法提供了一种非阻塞操作的机制，使I/O密集型或长时间运行的任务性能更好。
41. Explain what struct is in C# and how it differs from a class.
English: A struct in C# is a value type, which means it is stored on the stack and copies the entire value when assigned or passed. It is typically used for small, immutable data. A class, on the other hand, is a reference type stored on the heap and supports inheritance and polymorphism.
Chinese: C#中的struct是值类型，这意味着它存储在栈上，并在分配或传递时复制整个值。它通常用于小型不可变数据。另一方面，class是引用类型，存储在堆上，并支持继承和多态。
42. What is the difference between String and StringBuilder in C#?
English: String is immutable, meaning every time it is modified, a new object is created. StringBuilder is mutable and is designed to efficiently handle multiple string manipulations without creating new objects, making it more suitable for scenarios involving frequent modifications.
Chinese: String是不可变的，意味着每次修改时都会创建一个新对象。StringBuilder是可变的，旨在高效处理多次字符串操作而不创建新对象，这使其更适合频繁修改的场景。
43. How do you handle asynchronous exceptions in C#?
English: Asynchronous exceptions can be handled in C# using try-catch blocks in async methods or by using .ContinueWith() on tasks. It’s important to ensure proper exception handling to avoid unobserved task exceptions, which can crash the application.
Chinese: 可以通过在async方法中使用try-catch块或在任务上使用.ContinueWith()来处理C#中的异步异常。确保正确处理异常非常重要，以避免未观察到的任务异常导致应用程序崩溃。
44. Explain AutoMapper and its use in C#.
English: AutoMapper is a library in C# that automatically maps objects of different types. It is useful when you need to transfer data between objects like DTOs (Data Transfer Objects) and entities in an application, reducing the need for manual mapping code.
Chinese: AutoMapper是C#中的一个库，它可以自动映射不同类型的对象。当您需要在应用程序中的对象（如DTO（数据传输对象）和实体）之间传输数据时，它非常有用，减少了手动映射代码的需求。
45. What is deadlock, and how do you prevent it in C#?
English: A deadlock occurs when two or more threads are blocked forever, waiting for resources held by each other. Deadlocks can be prevented by acquiring locks in a consistent order, using timeout mechanisms, or by avoiding unnecessary locks.
Chinese: 当两个或多个线程永远阻塞，等待彼此持有的资源时，就会发生死锁。可以通过一致顺序获取锁、使用超时机制或避免不必要的锁来防止死锁。
46. What are property accessors in C#?
English: Property accessors (get and set) in C# provide a way to control access to class fields. The get accessor is used to return the property value, and the set accessor is used to assign a value, often with additional logic for validation or transformation.
Chinese: C#中的属性访问器（get和set）提供了一种控制类字段访问的方法。get访问器用于返回属性值，set访问器用于分配值，通常伴随有额外的逻辑来进行验证或转换。
47. What is Tuple in C#, and how is it used?
English: A Tuple in C# is a data structure that can store a fixed number of elements of different types. It’s useful for returning multiple values from a method without creating a custom class or struct. In C# 7 and later, ValueTuple provides better performance and named members.
Chinese: C#中的Tuple是一种数据结构，可以存储固定数量的不同类型的元素。它对于从方法返回多个值而无需创建自定义类或结构非常有用。在C# 7及更高版本中，ValueTuple提供了更好的性能和命名成员。
48. How does delegates differ from events in C#?
English: A delegate is a type that represents a reference to methods with a specific signature. An event is a special kind of delegate that restricts direct access, allowing only addition or removal of event handlers via += and -=, making it safer for external access.
Chinese: delegate是一种表示具有特定签名的方法引用的类型。event是一种特殊的委托，它限制了直接访问，只允许通过+=和-=添加或删除事件处理程序，使其对外部访问更加安全。
49. How does Task.WhenAll differ from Task.WhenAny in C#?
English: Task.WhenAll waits for all tasks to complete before continuing, while Task.WhenAny continues as soon as any one of the tasks has completed. Task.WhenAll is useful when all results are needed, and Task.WhenAny is useful when only the first result is required.
Chinese: Task.WhenAll等待所有任务完成后再继续，而Task.WhenAny在任意一个任务完成后继续执行。Task.WhenAll在需要所有结果时有用，而Task.WhenAny在只需要第一个结果时有用。
50. What is Polymorphism in C#, and how is it achieved?
English: Polymorphism in C# allows objects to be treated as instances of their base type, with the actual method called being determined by the object’s runtime type. It is achieved through method overriding (virtual and override keywords) and interfaces.
Chinese: C#中的多态性允许对象被视为其基类型的实例，实际调用的方法由对象的运行时类型决定。它通过方法重写（virtual和override关键字）和接口来实现。
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