.NET程序员技术面试问答管窥(二) —— C#
加国无忧 51.CA 2009年10月28日 16:31 来源：新职学院 作者：Qiao
- What’s the implicit name of the parameter that gets passed into the class’ set method?
Value, and its datatype depends on whatever variable we’re changing.
- How do you inherit from a class in C#?
Place a colon and then the name of the base class. Notice that it’s double colon in C++.
- Does C# support multiple inheritance?
No, use interfaces instead.
- When you inherit a protected class-level variable, who is it available to?
Classes in the same namespace.
- Describe the accessibility modifier protected internal.
It’s available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).
- What’s the top .NET class that everything is derived from?
- What does the keyword “virtual” mean in the method definition?
The method can be over-ridden.
- Can you declare the override method static while the original method is non-static?
No, you can’t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.
- Can you override private virtual methods?
No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.
- Can you prevent your class from being inherited or becoming a base class for some other classes?
Yes, that’s what keyword “sealed” in the class definition is for. The developer trying to derive from your class will get a message: cannot inherit from Sealed class XXX. It’s the same concept as “final” class in Java.
- Can you allow class to be inherited, but prevent the method from being over-ridden?
Yes, just leave the class public and make the method sealed.
- What’s an abstract class?
A class that cannot be instantiated. A concept in C++ known as pure virtual method. A class that must be inherited and have the methods over-ridden. Essentially, it’s a blueprint for a class without any implementation.
- What’s an interface class?
It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.
- Why can’t you specify the accessibility modifier for methods inside the interface?
They all must be public. Therefore, to prevent you from getting the false impression that you have any freedom of choice, you are not allowed to specify any accessibility, it’s “public” by default.
- Can you inherit multiple interfaces?
Yes, why not.
- What’s the difference between an interface and abstract class?
In the interface all methods must be abstract; in the abstract class some methods can be concrete. In the interface no accessibility modifiers are allowed, which is ok in abstract classes.
- How can you overload a method?
Different parameter data types, different number of parameters, different order of parameters.
- What’s the difference between overloading and overriding?
Overriding is done when the parent class method is overridden by a method of the same signature. Overloading is done in the same class on functions with input parameters differing in number or type. In overloading, there is a relationship between methods available in the same class; where as in overriding, there is relationship between a super class method and subclass method.
- What’s the advantage of using System.Text.StringBuilder over System.String?
StringBuilder is more efficient in the cases, where a lot of manipulation is done to the text. Strings are immutable, so each time it’s being operated on, a new instance is created.
- What’s the difference between the System.Array.CopyTo() and System.Array.Clone()?
The first one performs a deep copy of the array, the second one is shallow.
- How can you sort the elements of the array in descending order?
By calling Sort() and then Reverse() methods.
- What’s the .NET datatype that allows the retrieval of data by a unique key?
- What’s class SortedList underneath?
A sorted HashTable.
- Can multiple catch blocks be executed?
No, once the proper catch code fires off, the control is transferred to the finally block (if there are any), and then whatever follows the finally block.
- What’s a delegate?
A delegate object encapsulates a reference to a method. In C++ they were referred to as function pointers.
- What’s a multicast delegate?
It’s a delegate that points to and eventually fires off several methods.
- What are the ways to deploy an assembly?
An MSI installer, a CAB archive, and XCOPY command.
- What’s a satellite assembly?
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.
- What namespaces are necessary to create a localized application?
- What’s the difference between // comments and /// comments?
Single-line and XML documentation comments.
- Is XML case-sensitive?
Yes, so and are different elements.
- What debugging tools come with the .NET SDK?
CorDBG – command-line debugger, and DbgCLR – graphic debugger. Visual Studio .NET uses the DbgCLR. To use CorDbg, you must compile the original C# file using the /debug switch.
- What does the This window show in the debugger?
It points to the object that’s pointed to by this reference. Object’s instance data is shown.
- What does assert() do?
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.
- What’s the difference between the Debug class and Trace class?
Documentation looks the same. Use Debug class for debug builds, use Trace class for both debug and release builds.
- What are three test cases you should go through in unit testing?
Positive test cases (correct data, correct output), negative test cases (broken or missing data, proper handling), exception test cases (exceptions are thrown and caught properly).
- Explain the three services model (three-tier application).
Presentation (UI), business (logic and underlying code) and data (from storage or other sources).
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