转:C# Interview Questions
轉自: http://blogs.crsw.com/mark/articles/252.aspx
C# Interview Questions
This is a list of questions I have gathered from other sources?and created myself?over a period of time from my experience, many of which?I felt where incomplete or simply wrong.? I have finally taken the time to go through each question and correct them to the best of my ability.? However, please feel free to post feedback to challenge, improve, or suggest new questions.? I want to thank those of you that have contributed quality questions and corrections?thus far.
There are some question in this list that I do not consider to be good questions for an interview.? However, they do exist on other lists available on the Internet so I felt compelled to keep them easy access.
General Questions
No.
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It is available to any sub-class (a class inheriting this class).
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Yes, but they are not accessible.? Although they are not visible or accessible via the class interface, they are inherited.?
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It is available to classes that are within the same assembly and derived from the specified?base class.?
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System.Object.?
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The data value may not be changed.? Note: The variable value may be changed, but the original immutable data value was discarded and a new data value was created in memory.?
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System.String is immutable.? System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.?
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StringBuilder is more efficient in cases where there is a large amount of string manipulation.? Strings are immutable, so each time a string is changed,?a new instance in memory is created.
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No.?
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The Clone() method returns a new array (a shallow copy) object containing all the elements in the original array.? The CopyTo() method copies the elements into another existing array.? Both perform a shallow copy.? A shallow copy means the contents (each array element) contains references to the same object as the elements in the original array.? A deep copy (which neither of these methods performs) would create a new instance of each element's object, resulting in a different, yet identacle object.
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By calling Sort() and then Reverse() methods.?
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HashTable.?
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A sorted HashTable.?
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Yes.
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A catch block that catches the exception of type System.Exception.? You can also omit the parameter data type in this case and just write catch {}.?
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No.? Once the proper catch block processed, control is transferred to the finally block (if there are any).?
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Presentation (UI), Business (logic and underlying code) and Data (from storage or other sources).?
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Class Questions
Place a colon and then the name of the base class.
Example: class MyNewClass : MyBaseClass?
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Yes.? The keyword “sealed” will prevent the class from being inherited.?
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Yes.? Just leave the class public and make the method sealed.?
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A class that cannot be instantiated. ?An abstract class is a class that must be inherited and have the methods overridden. ?An abstract class is essentially a blueprint for a class without any implementation.?
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1. When the class itself is inherited from an abstract class, but not all base abstract methods have been overridden.
2.? When at least one of the methods in the class is abstract.?
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Interfaces, like classes, define a set of properties, methods, and events. But unlike classes, interfaces do not provide implementation. They are implemented by classes, and defined as separate entities from classes.?
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They all must be public, and are therefore public by default.?
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Yes.? .NET does support multiple interfaces.?
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It’s up to you to implement the method inside your own class, so implementation is left entirely up to you. This might cause a problem on a higher-level scale if similarly named methods from different interfaces expect different data, but as far as compiler cares you’re okay.
To Do: Investigate?
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In an interface class, all methods are abstract - there is no implementation.? In an abstract class some methods can be concrete. ?In an interface class, no accessibility modifiers are allowed.? An abstract class may have accessibility modifiers.?
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Structs are value-type variables and are thus saved on the stack, additional overhead but faster retrieval.? Another difference is that structs?cannot inherit.?
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Method and Property Questions
Value.? The data type of the value parameter is defined by whatever data type the property is declared as.?
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The method or property can be overridden.?
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When overriding a method, you change the behavior of the method for the derived class.? Overloading a method simply involves having another method with the same name within the class.?
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No.? The signature of the virtual method must remain the same.? (Note: Only the keyword virtual is changed to keyword override)?
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Different parameter data types, different number of parameters, different order of parameters.?
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Yes, just place a colon, and then keyword base (parameter list to invoke the appropriate constructor) in the overloaded constructor definition inside the inherited class.
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Events and Delegates
A delegate object encapsulates a reference to a method.?
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A delegate that has multiple handlers assigned to it.? Each assigned handler (method) is called.
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XML Documentation Questions
Yes.?
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Single-line comments, multi-line comments, and XML documentation comments.?
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Compile it with the /doc switch.
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Debugging and Testing Questions
1.?? CorDBG – command-line debugger.? To use CorDbg, you must compile the original C# file using the /debug switch.
2.?? DbgCLR – graphic debugger. ?Visual Studio .NET uses the DbgCLR.?
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In debug compilation, assert takes in a Boolean condition as a parameter, and shows the error dialog if the condition is false. ?The program proceeds without any interruption if the condition is true.?
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Documentation looks the same. ?Use Debug class for debug builds, use Trace class for both debug and release builds.?
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The tracing dumps can be quite verbose.? For applications that are constantly running you run the risk of overloading the machine and the hard drive. ?Five levels range from None to Verbose, allowing you to fine-tune the tracing activities.?
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To the Console or a text file depending on the parameter passed to the constructor.?
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Attach the aspnet_wp.exe process to the DbgClr debugger.?
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1.?????? Positive test cases (correct data, correct output).
2.?????? Negative test cases (broken or missing data, proper handling).
3.?????? Exception test cases (exceptions are thrown and caught properly).?
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Yes.? If you are debugging via Visual Studio.NET, just go to Immediate window.?
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ADO.NET and Database Questions
What is the role of the DataReader class in ADO.NET connections?
It returns a read-only, forward-only rowset from the data source.? A DataReader provides fast access when a forward-only sequential read is needed.?
?What are advantages and disadvantages of Microsoft-provided data provider classes in ADO.NET?
SQLServer.NET data provider is high-speed and robust, but requires SQL Server license purchased from Microsoft. OLE-DB.NET is universal for accessing other sources, like Oracle, DB2, Microsoft Access and Informix.? OLE-DB.NET is a .NET layer on top of the OLE layer, so it’s not as fastest and efficient as SqlServer.NET.?
? What is the wildcard character in SQL?
Let’s say you want to query database with LIKE for all employees whose name starts with La.The wildcard character is %, the proper query with LIKE would involve ‘La%’.?
? Explain ACID rule of thumb for transactions.
A transaction must be:
1.?????? Atomic - it is one unit of work and does not dependent on previous and following transactions.
2.?????? Consistent - data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t.
3.?????? Isolated - no transaction sees the intermediate results of the current transaction).
4.?????? Durable - the values persist if the data had been committed even if the system crashes right after.?
? What connections does Microsoft SQL Server support?
Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and password).?
? Between Windows Authentication and SQL Server Authentication, which one is trusted and which one is untrusted?
Windows Authentication is trusted because the username and password are checked with the Active Directory, the SQL Server authentication is untrusted, since SQL Server is the only verifier participating in the transaction.?
? What does the Initial Catalog parameter define in the connection string?
The database name to connect to.?
?What does the Dispose method do with the connection object?
Deletes it from the memory.
To Do: answer better.? The current answer is not entirely correct.?
? What is a pre-requisite for connection pooling?
Multiple processes must agree that they will share the same connection, where every parameter is the same, including the security settings.The connection string must be identical.
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Assembly Questions
Assembly versioning allows the application to specify not only the library it needs to run (which was available under Win32), but also the version of the assembly.?
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An MSI installer, a CAB archive, and XCOPY command.?
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When you write a multilingual or multi-cultural application in .NET, and want to distribute the core application separately from the localized modules, the localized assemblies that modify the core application are called satellite assemblies.?
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System.Globalization and System.Resources.
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an Assembly.
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As a good rule, you should not call the garbage collector.? However, you?could call the garbage collector when you are done using a large object (or set of objects) to force the garbage collector to dispose of those very large objects from memory.? However, this is usually not a good practice.
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Use Boxing.
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Boxing converts?a value-type to a reference-type, thus storing the object on the heap.? Unboxing converts a reference-type to a value-type, thus storing the value on the stack.
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轉載于:https://www.cnblogs.com/skyfei/archive/2009/11/10/1599720.html
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