C# Realtime Interview Questions and Answers
What is delay signing?
Delay signing allows you to place a shared assembly in the GAC by signing the assembly with just the public key. This allows the assembly to be signed with the private key at a later stage, when the development process is complete and the component or assembly is ready to be deployed. This process enables developers to work with shared assemblies as if they were strongly named, and it secures the private key of the signature from being accessed at different stages of development.
Is there an equivalent of exit() for quitting a C# .NET application?
Yes, you can use System.Environment.Exit(int exitCode) to exit the application or Application.Exit() if it's a Windows Forms app.
Can you prevent your class from being inherited and becoming a base class for some other classes?
Yes, that is 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 is the same concept as final class in Java.
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.
I was trying to use an "out int" parameter in one of my functions. How should I declare the variable that I am passing to it?
You should declare the variable as an int, but when you pass it in you must specify it as 'out', like the following:
int i;
foo(out i);
where foo is declared as follows:
[return-type] foo(out int o) { }
How do I make a DLL in C#?
You need to use the /target:library compiler option.
Is XML case-sensitive?
Yes, so and are different elements.
How do I simulate optional parameters to COM calls?
You must use the Missing class and pass Missing.Value (in System.Reflection) for any values that have optional parameters.
Will finally block get executed if the exception had not occurred?
Yes.
What is the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception? Does C# support try-catch-finally blocks?
Yes. Try-catch-finally blocks are supported by the C# compiler. Here's an example of a try-catch-finally block:
using System;
public class TryTest
{
static void Main()
{
try
{
Console.WriteLine("In Try block");
throw new ArgumentException();
}
catch(ArgumentException n1)
{
Console.WriteLine("Catch Block");
}
finally
{
Console.WriteLine("Finally Block");
}
}
}
Output: In Try Block
Catch Block
Finally Block
If I return out of a try/finally in C#, does the code in the finally-clause run? Yes. The code in the finally always runs. If you return out of the try block, or even if you do a "goto" out of the try, the finally block always runs, as shown in the following
example:
using System;
class main
{
public static void Main()
{
try
{
Console.WriteLine("In Try block");
return;
}
finally
{
Console.WriteLine("In Finally block");
}
}
}
Both "In Try block" and "In Finally block" will be displayed. Whether the return is in the try block or after the try-finally block, performance is not affected either way. The compiler treats it as if the return were outside the try block anyway. If it's a return without an expression (as it is above), the IL emitted is identical whether the return is inside or outside of the try. If the return has an expression, there's an extra store/load of the value of the expression (since it has to be computed within the try block).
Is there a way to force garbage collection?
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().
Is there regular expression (regex) support available to C# developers?
Yes. The .NET class libraries provide support for regular expressions. Look at the documentation for the System.Text.RegularExpressions namespace.
Does C# support properties of array types?
Yes. Here's a simple example: using System;
class Class1
{
private string[] MyField;
public string[] MyProperty
{
get { return MyField; }
set { MyField = value; }
}
}
class MainClass
{
public static int Main(string[] args)
{
Class1 c = new Class1();
string[] arr = new string[] {"apple", "banana"};
c.MyProperty = arr;
Console.WriteLine(c.MyProperty[0]); // "apple"
return 0;
}
}
What connections does Microsoft SQL Server support?
Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords)
When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)?
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.
Why would you use untrusted verification?
Web Services might use it, as well as non-Windows applications.
How is 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 is the implicit name of the parameter that gets passed into the class set method?
Value, and its datatype depends on whatever variable we are changing.
How do I register my code for use by classic COM clients?
Use the regasm.exe utility to generate a type library (if needed) and the necessary entries in the Windows Registry to make a class available to classic COM clients. Once a class is registered in the Windows Registry with regasm.exe, a COM client can use the class as though it were a COM class
What is the top .NET class that everything is derived from?
System.Objects
What is an abstract class?
The abstract modifier can be used with classes, methods, properties, indexers, and events.
Use the abstract modifier in a class declaration to indicate that a class is intended only to be a base class of other classes.
Abstract classes have the following features:
An abstract class cannot be instantiated.
An abstract class may contain abstract methods and accessors.
It is not possible to modify an abstract class with the sealed modifier, which means that the class cannot be inherited.
A non-abstract class derived from an abstract class must include actual implementations of all inherited abstract methods and accessors.
Use the abstract modifier in a method or property declaration to indicate that the method or property does not contain implementation.
Abstract methods have the following features:
An abstract method is implicitly a virtual method.
Abstract method declarations are only permitted in abstract classes.
Because an abstract method declaration provides no actual implementation, there is no method body; the method declaration simply ends with a semicolon and there are no braces ({ }) following the signature. For example:
public abstract void MyMethod();
________________________________________
abstract class is a prototype of a class. it is used to provide partial
class implementation. abstract class contain abstract method which can be implemented by derived class.
some rules for abstract class are following-:
1) an object of an abstract class can never be created.
2)you can not declare an abstract method outside the abstract class.
3)can not be declared sealed.
WHAT IS THE ADVANTAGE OF SERIALIZATION?
Serialization is the process of maintaing object in the form stream. it is useful in case of remoting.
Serialization is the process of converting object into byte stream which is useful to transport object(i.e remoting),persisting object(i.e files,database)
SERIALIZATION IS PROCESS OF LOADING THE OBJECT STATE IN THE FORM OF BYTE STREAMS IN DATABASE/FILE SYATEM.
Can we inherit the java class in C# class,how?
Java Programming language is not supported with .Net Framework hence you cannot inherit javaclass in C# class.Also Java has JavaByte code after compiling similar to MSIL which is similar but cannot inherit due to framework support.
Are C# destructors the same as C++ destructors?
No. They look the same but they are very different. The C# destructor syntax (with the familiar ~ character) is just syntactic sugar for an override of the System.Object Finalize method. This Finalize method is called by the garbage collector when it determines that an object is no longer referenced, before it frees the memory associated with the object. So far this sounds like a C++ destructor. The difference is that the garbage collector makes no guarantees about when this procedure happens. Indeed, the algorithm employed by the CLR garbage collector means that it may be a long time after the application has finished with the object. This lack of certainty is often termed ‘non-deterministic finalization’, and it means that C# destructors are not suitable for releasing scarce resources such as database connections, file handles etc.
To achieve deterministic destruction, a class must offer a method to be used for the purpose. The standard approach is for the class to implement the IDisposable interface. The user of the object must call the Dispose() method when it has finished with the object. C# offers the ‘using’ construct to make this easier.
What is wrapper class? is it available in c#?
Wrapper Classes are the classes that wrap up the primitive values in to a class that offer utility method to access it . For eg you can store list of int values in a vector class and access the class. Also the methods are static and hence you can use them without creating an instance . The values are immutable .
wrapper class are those class in which we can not define and call all predefined function .it is possible in java not C#.
Which tool is used to browse the classes, structs, interfaces etc. in the BCL?
wincv as in Windows Class View
How is the using() pattern useful? What is IDisposable? How does it support deterministic finalization?
The using() pattern is useful because it ensures that Dispose() will always be called when a disposable object (defined as one that implements IDisposable, and thus the Dispose() method) goes out of scope, even if it does so by an exception being thrown, and thus that resources are always released.
What happens when a C# project has more than 1 Main methods
f the project is compiled using /main switch with the compiler then the project compiles successfully.
For example:
class A
{
public static void Main(string[] args)
{
Console.WriteLine("Main in class A");
}
}
class B
{
public static void Main(string[] args)
{
Console.WriteLine("Main in class B");
}
}
Now compile with the /main switch with the C# compiler like
csc MultipleMain.cs /main:A
This will compile without error and while executing it will show Main in class A
Attempting to compile an application consisting of multiple classes with defined Main methods and not specifying the /main switch will result in a compiler error.
How do you refer parent classes in C#? A) Super B) This C) Base
This keyword is used for reffering current object and Base keyword is used for referring parrent class. so ans. is C.
Super: Super is used to Refer the Base Class in JAVA
This: This is used to Refer the Current or Child Class in C#
Base: Base is used to Refer The Parent or Base Class
What is object pooling
Defination: A performance optimization based on using collections of pre-allocated resources, such as objects or database connections
With the advent of the .NET platform, writing code that pools objects and threads has become a simple task. By using the Threading and Collections namespaces, you can create robust object pooling applications. This could also be done by implementing COM+ interop interfaces into your code.
Which method is actually called ultimately when Console.WriteLine( ) is invoked?
A) Append( )
B) AppendFormat( )
C) Tostring( )
Ans: B, AppendFormat() method is called.
What is an Assembly?
An assembly is a file that is automatically generated by the compiler upon successful compilation of every .NET application. It can be either a Dynamic Link Library or an executable file. It is generated only once for an application and upon each subsequent compilation the assembly gets updated. The entire process will run in the background of your application; there is no need for you to learn deeply about assemblies. However, a basic knowledge about this topic will help you to understand the architecture behind a .NET application.
An assembly is used by the .NET CLR (Common Language Runtime) as the smallest unit for: deployment; version control; security; type grouping and code reuse. Assemblies consists of a manifest and one or more modules and/or files like HTML, XML, images, video clips,...
An assembly can be thought of as a logical DLL and must contain a single manifest and may optionally contain type meta data, MSIL (Microsoft Intermediate Language) and resources.
Assemblies come in 2 flavors: application private and shared. Application private assemblies are used by one application only. This is the default style of assembly. Such assemblies must reside in the application folder.
Shared assemblies are meant to be used by more than one application. They must have a
globally unique name and must be defined in the GAC (Global Assembly Cache). To learn more about viewing the GAC
Basically there are two kind of assemblies when it comes to deployment.
Private Assemblies
Shared Assemblies
Private assemblies are the ones which are in your application folder itself. They can be easily and uniquely identified by their name.
These type of assemblies can be deployed simply by copying them to the bin folder of your application.
Shared Assemblies are those which can be shared by multiple applications on the machine.
For this we have to place the Shared assembly in the GAC.
Now since we can install any application or assembly created by any company, that is we install assemblies from oracle, microsoft and similarly from many other companies.
There is always a possiblity that they may use the same assembly name as your assembly name.
If such type of assemblies are placed in the GAC then we cannot uniquely identify a particular assembly.But if we give a strong name to the assmebly then it is like a unique identifier for the assembly.It is Globally unique.
Strong name consists of
1. Name of the assembly
2. Public key token
3. optionally any resources
4. Version Number
So basically to uniquely identify a particular assembly from the GAC we have to give it a strong name. Its that simple.
The Shared assembly can be deployed in to GAC by using the GACUTIL tool with the -i switch
gacutil -i assemblyname
or simply copying it to the assembly folder in the windows directory (XP) or WINNT directory(others)
Also there are Satellite Assemblies which contian only resources like strings, images etc.
Also there are dynamic assemblies which are generated on the fly dynamically.
What is delay signing?
Delay signing allows you to place a shared assembly in the GAC by signing the assembly with just the public key. This allows the assembly to be signed with the private key at a later stage, when the development process is complete and the component or assembly is ready to be deployed. This process enables developers to work with shared assemblies as if they were strongly named, and it secures the private key of the signature from being accessed at different stages of development.
Is there an equivalent of exit() for quitting a C# .NET application?
Yes, you can use System.Environment.Exit(int exitCode) to exit the application or Application.Exit() if it's a Windows Forms app.
Can you prevent your class from being inherited and becoming a base class for some other classes?
Yes, that is 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 is the same concept as final class in Java.
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.
I was trying to use an "out int" parameter in one of my functions. How should I declare the variable that I am passing to it?
You should declare the variable as an int, but when you pass it in you must specify it as 'out', like the following:
int i;
foo(out i);
where foo is declared as follows:
[return-type] foo(out int o) { }
How do I make a DLL in C#?
You need to use the /target:library compiler option.
Is XML case-sensitive?
Yes, so and are different elements.
How do I simulate optional parameters to COM calls?
You must use the Missing class and pass Missing.Value (in System.Reflection) for any values that have optional parameters.
Will finally block get executed if the exception had not occurred?
Yes.
What is the C# equivalent of C++ catch (…), which was a catch-all statement for any possible exception? Does C# support try-catch-finally blocks?
Yes. Try-catch-finally blocks are supported by the C# compiler. Here's an example of a try-catch-finally block:
using System;
public class TryTest
{
static void Main()
{
try
{
Console.WriteLine("In Try block");
throw new ArgumentException();
}
catch(ArgumentException n1)
{
Console.WriteLine("Catch Block");
}
finally
{
Console.WriteLine("Finally Block");
}
}
}
Output: In Try Block
Catch Block
Finally Block
If I return out of a try/finally in C#, does the code in the finally-clause run? Yes. The code in the finally always runs. If you return out of the try block, or even if you do a "goto" out of the try, the finally block always runs, as shown in the following
example:
using System;
class main
{
public static void Main()
{
try
{
Console.WriteLine("In Try block");
return;
}
finally
{
Console.WriteLine("In Finally block");
}
}
}
Both "In Try block" and "In Finally block" will be displayed. Whether the return is in the try block or after the try-finally block, performance is not affected either way. The compiler treats it as if the return were outside the try block anyway. If it's a return without an expression (as it is above), the IL emitted is identical whether the return is inside or outside of the try. If the return has an expression, there's an extra store/load of the value of the expression (since it has to be computed within the try block).
Is there a way to force garbage collection?
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().
Is there regular expression (regex) support available to C# developers?
Yes. The .NET class libraries provide support for regular expressions. Look at the documentation for the System.Text.RegularExpressions namespace.
Does C# support properties of array types?
Yes. Here's a simple example: using System;
class Class1
{
private string[] MyField;
public string[] MyProperty
{
get { return MyField; }
set { MyField = value; }
}
}
class MainClass
{
public static int Main(string[] args)
{
Class1 c = new Class1();
string[] arr = new string[] {"apple", "banana"};
c.MyProperty = arr;
Console.WriteLine(c.MyProperty[0]); // "apple"
return 0;
}
}
What connections does Microsoft SQL Server support?
Windows Authentication (via Active Directory) and SQL Server authentication (via Microsoft SQL Server username and passwords)
When do you absolutely have to declare a class as abstract (as opposed to free-willed educated choice or decision based on UML diagram)?
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.
Why would you use untrusted verification?
Web Services might use it, as well as non-Windows applications.
How is 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 is the implicit name of the parameter that gets passed into the class set method?
Value, and its datatype depends on whatever variable we are changing.
How do I register my code for use by classic COM clients?
Use the regasm.exe utility to generate a type library (if needed) and the necessary entries in the Windows Registry to make a class available to classic COM clients. Once a class is registered in the Windows Registry with regasm.exe, a COM client can use the class as though it were a COM class
What is the top .NET class that everything is derived from?
System.Objects
What is an abstract class?
The abstract modifier can be used with classes, methods, properties, indexers, and events.
Use the abstract modifier in a class declaration to indicate that a class is intended only to be a base class of other classes.
Abstract classes have the following features:
An abstract class cannot be instantiated.
An abstract class may contain abstract methods and accessors.
It is not possible to modify an abstract class with the sealed modifier, which means that the class cannot be inherited.
A non-abstract class derived from an abstract class must include actual implementations of all inherited abstract methods and accessors.
Use the abstract modifier in a method or property declaration to indicate that the method or property does not contain implementation.
Abstract methods have the following features:
An abstract method is implicitly a virtual method.
Abstract method declarations are only permitted in abstract classes.
Because an abstract method declaration provides no actual implementation, there is no method body; the method declaration simply ends with a semicolon and there are no braces ({ }) following the signature. For example:
public abstract void MyMethod();
________________________________________
abstract class is a prototype of a class. it is used to provide partial
class implementation. abstract class contain abstract method which can be implemented by derived class.
some rules for abstract class are following-:
1) an object of an abstract class can never be created.
2)you can not declare an abstract method outside the abstract class.
3)can not be declared sealed.
WHAT IS THE ADVANTAGE OF SERIALIZATION?
Serialization is the process of maintaing object in the form stream. it is useful in case of remoting.
Serialization is the process of converting object into byte stream which is useful to transport object(i.e remoting),persisting object(i.e files,database)
SERIALIZATION IS PROCESS OF LOADING THE OBJECT STATE IN THE FORM OF BYTE STREAMS IN DATABASE/FILE SYATEM.
Can we inherit the java class in C# class,how?
Java Programming language is not supported with .Net Framework hence you cannot inherit javaclass in C# class.Also Java has JavaByte code after compiling similar to MSIL which is similar but cannot inherit due to framework support.
Are C# destructors the same as C++ destructors?
No. They look the same but they are very different. The C# destructor syntax (with the familiar ~ character) is just syntactic sugar for an override of the System.Object Finalize method. This Finalize method is called by the garbage collector when it determines that an object is no longer referenced, before it frees the memory associated with the object. So far this sounds like a C++ destructor. The difference is that the garbage collector makes no guarantees about when this procedure happens. Indeed, the algorithm employed by the CLR garbage collector means that it may be a long time after the application has finished with the object. This lack of certainty is often termed ‘non-deterministic finalization’, and it means that C# destructors are not suitable for releasing scarce resources such as database connections, file handles etc.
To achieve deterministic destruction, a class must offer a method to be used for the purpose. The standard approach is for the class to implement the IDisposable interface. The user of the object must call the Dispose() method when it has finished with the object. C# offers the ‘using’ construct to make this easier.
What is wrapper class? is it available in c#?
Wrapper Classes are the classes that wrap up the primitive values in to a class that offer utility method to access it . For eg you can store list of int values in a vector class and access the class. Also the methods are static and hence you can use them without creating an instance . The values are immutable .
wrapper class are those class in which we can not define and call all predefined function .it is possible in java not C#.
Which tool is used to browse the classes, structs, interfaces etc. in the BCL?
wincv as in Windows Class View
How is the using() pattern useful? What is IDisposable? How does it support deterministic finalization?
The using() pattern is useful because it ensures that Dispose() will always be called when a disposable object (defined as one that implements IDisposable, and thus the Dispose() method) goes out of scope, even if it does so by an exception being thrown, and thus that resources are always released.
What happens when a C# project has more than 1 Main methods
f the project is compiled using /main switch with the compiler then the project compiles successfully.
For example:
class A
{
public static void Main(string[] args)
{
Console.WriteLine("Main in class A");
}
}
class B
{
public static void Main(string[] args)
{
Console.WriteLine("Main in class B");
}
}
Now compile with the /main switch with the C# compiler like
csc MultipleMain.cs /main:A
This will compile without error and while executing it will show Main in class A
Attempting to compile an application consisting of multiple classes with defined Main methods and not specifying the /main switch will result in a compiler error.
How do you refer parent classes in C#? A) Super B) This C) Base
This keyword is used for reffering current object and Base keyword is used for referring parrent class. so ans. is C.
Super: Super is used to Refer the Base Class in JAVA
This: This is used to Refer the Current or Child Class in C#
Base: Base is used to Refer The Parent or Base Class
What is object pooling
Defination: A performance optimization based on using collections of pre-allocated resources, such as objects or database connections
With the advent of the .NET platform, writing code that pools objects and threads has become a simple task. By using the Threading and Collections namespaces, you can create robust object pooling applications. This could also be done by implementing COM+ interop interfaces into your code.
Which method is actually called ultimately when Console.WriteLine( ) is invoked?
A) Append( )
B) AppendFormat( )
C) Tostring( )
Ans: B, AppendFormat() method is called.
What is an Assembly?
An assembly is a file that is automatically generated by the compiler upon successful compilation of every .NET application. It can be either a Dynamic Link Library or an executable file. It is generated only once for an application and upon each subsequent compilation the assembly gets updated. The entire process will run in the background of your application; there is no need for you to learn deeply about assemblies. However, a basic knowledge about this topic will help you to understand the architecture behind a .NET application.
An assembly is used by the .NET CLR (Common Language Runtime) as the smallest unit for: deployment; version control; security; type grouping and code reuse. Assemblies consists of a manifest and one or more modules and/or files like HTML, XML, images, video clips,...
An assembly can be thought of as a logical DLL and must contain a single manifest and may optionally contain type meta data, MSIL (Microsoft Intermediate Language) and resources.
Assemblies come in 2 flavors: application private and shared. Application private assemblies are used by one application only. This is the default style of assembly. Such assemblies must reside in the application folder.
Shared assemblies are meant to be used by more than one application. They must have a
globally unique name and must be defined in the GAC (Global Assembly Cache). To learn more about viewing the GAC
Basically there are two kind of assemblies when it comes to deployment.
Private Assemblies
Shared Assemblies
Private assemblies are the ones which are in your application folder itself. They can be easily and uniquely identified by their name.
These type of assemblies can be deployed simply by copying them to the bin folder of your application.
Shared Assemblies are those which can be shared by multiple applications on the machine.
For this we have to place the Shared assembly in the GAC.
Now since we can install any application or assembly created by any company, that is we install assemblies from oracle, microsoft and similarly from many other companies.
There is always a possiblity that they may use the same assembly name as your assembly name.
If such type of assemblies are placed in the GAC then we cannot uniquely identify a particular assembly.But if we give a strong name to the assmebly then it is like a unique identifier for the assembly.It is Globally unique.
Strong name consists of
1. Name of the assembly
2. Public key token
3. optionally any resources
4. Version Number
So basically to uniquely identify a particular assembly from the GAC we have to give it a strong name. Its that simple.
The Shared assembly can be deployed in to GAC by using the GACUTIL tool with the -i switch
gacutil -i assemblyname
or simply copying it to the assembly folder in the windows directory (XP) or WINNT directory(others)
Also there are Satellite Assemblies which contian only resources like strings, images etc.
Also there are dynamic assemblies which are generated on the fly dynamically.
