.Net Framework Interview Questions 7

By | May 13, 2014

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.

Why are there five tracing levels in System.Diagnostics.TraceSwitcher? The tracing dumps can be quite verbose and for some applications that are constantly running you run the risk of overloading the machine and the hard drive there. Five levels range from None to Verbose, allowing to fine-tune the tracing activities.

Where is the output of TextWriterTraceListener redirected? To the Console or a text file depending on the parameter passed to the constructor.

What namespaces are necessary to create a localized application? System.Globalization, System.Resources.

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).

Can you change the value of a variable while debugging a C# application? Yes, if you are debugging via Visual Studio.NET, just go to Immediate window.

What’s the implicit name of the parameter that gets passed into the class’ set method? Value, and it’s 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? Derived Classes.

What’s the top .NET class that everything is derived from? System.Object.

How’s method overriding different from overloading? When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the  same name within the class.

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 and 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 WhateverBaseClassName. 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.

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.

And if they have conflicting method names? 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.

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.

If a base class has a bunch of overloaded constructors, and an inherited class has another bunch of overloaded constructors, can you enforce a call from an inherited constructor to an arbitrary base constructor? 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.

What’s the difference between System.String and System.StringBuilder classes? System.String is immutable, System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

Does C# support multiple-inheritance? No, use interfaces instead.

When you inherit a protected class-level variable, who is it available to? The derived class.

Are private class-level variables inherited? Yes, but they are not accessible.  Although they are not visible or accessible via the class interface, they are inherited.

Describe the accessibility modifier “protected internal”. It is 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? System.Object.

What’s the advantage of using System.Text.StringBuilder over System.String? StringBuilder is more efficient in cases where there is a large amount of string manipulation.  Strings are immutable, so each time it’s being operated on, a new instance is created.

Can you store multiple data types in System.Array? No.

What’s the .NET class that allows the retrieval of a data element using a unique key? HashTable.

Will the finally block get executed if an exception has not occurred? Yes.

What’s an abstract class? 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.

When do you absolutely have to declare a class as abstract?
1.       When at least one of the methods in the class is abstract.
2.       When the class itself is inherited from an abstract class, but not all base abstract methods have been overridden.

What’s an interface? 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.

What’s the difference between an interface and abstract class? In an interface class, all methods must be abstract.  In an abstract class some methods can be concrete.  In an interface class, no accessibility modifiers are allowed, which is ok in an abstract class.

How is method overriding different from method overloading? 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.

Can you declare an override method to be static if the original method is non-static? No. 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.  Private methods are not accessible outside the class.

Can you write a class without specifying namespace? Which namespace does it belong to by default?  Yes, you can, then the class belongs to global namespace which has no name. For commercial products, naturally, you  wouldn’t want global namespace.

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