Interview - 1

Front 1

Are private class-level variables inherited?

Back 1

Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.

Front 2

Why does DllImport not work for me?

Back 2

All methods marked with the DllImport attribute must be marked as public static extern

Front 3

Why does my Windows application pop up a console window every time I run it?

Back 3

Make sure that the target type set in the project properties setting is set to Windows Application, and not Console Application. If you’re using the command line, compile with /target:winexe, not /target:exe.

Front 4

Why do I get a security exception when I try to run my C# app?

Back 4

Some security exceptions are thrown if you are working on a network share. There are some parts of the frameworks that will not run if being run off a share (roaming profile, mapped drives, etc.). To see if this is what’s happening, just move the executable over to your local drive and see if it runs without the exceptions. One of the common exceptions thrown under these conditions is System.Security.SecurityException. To get around this, you can change your security policy for the intranet zone, code group 1.2, (the zone that running off shared folders falls into) by using the caspol.exe tool.

Front 5

What is the difference between a struct and a class in C#?

Back 5

Structs differ from classes in several important ways; however, structs are value types rather than reference types, and inheritance is not supported for structs. Struct values are stored on the stack or in-line. Careful programmers can sometimes enhance performance through judicious use of structs. For example, the use of a struct rather than a class for a Point can make a large difference in the number of memory allocations performed at runtime. The program below creates and initializes an array of 100 points. With Point implemented as a class, 101 separate objects are instantiated-one for the array and one each for the 100 elements.

Front 6

Is there an equivalent of exit() for quitting a C# .NET application?

Back 6

Yes, you can use System.Environment.Exit(int exitCode) to exit the application or Application.Exit() if it’s a Windows Forms app.

Front 7

Is there a way to force garbage collection?

Back 7

Yes. Set all references to null and then call System.GC.Collect(). If you need to have some objects destructed, and System.GC.Collect() doesn’t seem to be doing it for you, you can force finalizers to be run by setting all the references to the object to null and then calling System.GC.RunFinalizers().

Front 8

What’s the implicit name of the parameter that gets passed into the class’ set method?

Back 8

Value, and it’s datatype depends on whatever variable we’re changing.

Front 9

How do you inherit from a class in C#?

Back 9

Place a colon and then the name of the base class.

Front 10

Does C# support multiple inheritance?

Back 10

No, use interfaces instead.

Front 11

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

Back 11

Classes in the same namespace.

Front 12

Are private class-level variables inherited?

Back 12

Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.

Front 13

Describe the accessibility modifier protected internal.

Back 13

It’s available to derived classes and classes within the same Assembly (and naturally from the base class it’s declared in).

Front 14

C# provides a default constructor for me. I write a constructor that takes a string as a parameter, but want to keep the no parameter one. How many constructors should I write?

Back 14

Two. Once you write at least one constructor, C# cancels the freebie constructor, and now you have to write one yourself, even if there’s no implementation in it.

Front 15

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

Back 15

System.Object.

Front 16

How’s method overriding different from overloading?

Back 16

When overriding, you change the method behavior for a derived class. Overloading simply involves having a method with the same name within the class.

Front 17

What does the keyword virtual mean in the method definition

Back 17

The method can be overridden.

Front 18

Can you declare the override method static while the original method is non-static?

Back 18

No, you can’t, the signature of the virtual method must remain the same, only the keyword virtual is changed to keyword override.

Front 19

Can you override private virtual methods?

Back 19

No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access.

Front 20

Can you prevent your class from being inherited and becoming a base class for some other classes?

Back 20

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.

Front 21

Can you allow class to be inherited, but prevent the method from being over-ridden?

Back 21

Yes, just leave the class public and make the method sealed.

Front 22

What’s an abstract class?

Back 22

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.

Front 23

When do you absolutely have to declare a class as abstrac

Back 23

When at least one of the methods in the class is abstract. When the class itself is inherited from an abstract class, but not all base abstract methods have been over-ridden.

Front 24

What’s an interface class?

Back 24

It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes.

Front 25

Why can’t you specify the accessibility modifier for methods inside the interface?

Back 25

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.

Front 26

Can you inherit multiple interfaces?

Back 26

Yes, why not.

Front 27

And if they have (multiple interfaces) conflicting method names

Back 27

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.

Front 28

What’s the difference between an interface and abstract class?

Back 28

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.

Front 29

How can you overload a method?

Back 29

Different parameter data types, different number of parameters, different order of parameters.

Front 30

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?

Back 30

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.

Front 31

What’s the difference between System.String and System.StringBuilder classes?

Back 31

System.String is immutable, System.StringBuilder was designed with the purpose of having a mutable string where a variety of operations can be performed.

Front 32

Is it namespace class or class namespace?

Back 32

The .NET class library is organized into namespaces. Each namespace contains a functionally related group of classes so natural namespace comes first.