C Sharp Interview Questions
- 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.
- Are private class-level
variables inherited?
Yes, but they are not accessible, so looking at it you can honestly say that they are not inherited. But they are.
- 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).
- 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?
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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Can
you store multiple data types in System.Array?
No.
- 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?
HashTable.
- What’s class
SortedList underneath?
A sorted HashTable.
- Will
finally block get executed if the exception had not occurred?
Yes.
- What’s the
C# equivalent of C++ catch (…), which was a catch-all statement for
any possible exception?
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 {}.
- 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.
- Why is it a
bad idea to throw your own exceptions?
Well, if at that point you know that an error has occurred, then why not write the proper code to handle that error instead of passing a new Exception object to the catch block? Throwing your own exceptions signifies some design flaws in the project.
- 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.
- How’s the
DLL Hell problem solved in .NET?
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.
- 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?
System.Globalization, System.Resources.
- What’s the
difference between // comments, /* */ comments and /// comments?
Single-line, multi-line and XML documentation comments.
- How do you generate
documentation from the C# file commented properly with a command-line
compiler?
Compile it with a /doc switch.
- What’s the
difference between <c> and <code> XML documentation tag?
Single line code example and multiple-line code example.
- Is XML case-sensitive?
Yes, so <Student> and <student> 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.
- 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.
- How do you debug
an ASP.NET Web application?
Attach the aspnet_wp.exe process to the DbgClr debugger.
- 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.
- Explain the
three services model (three-tier application).
Presentation (UI), business (logic and underlying code) and data (from storage or other sources).
- 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, but it’s a .NET layer on top of OLE layer, so not the fastest thing in the world. ODBC.NET is a deprecated layer provided for backward compatibility to ODBC engines.
- What’s the
role of the DataReader class in ADO.NET connections?
It returns a read-only dataset from the data source when the command is executed.
- 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.
Transaction must be Atomic (it is one unit of work and does not dependent on previous and following transactions), Consistent (data is either committed or roll back, no “in-between” case where something has been updated and something hasn’t), Isolated (no transaction sees the intermediate results of the current transaction), 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 passwords).
- 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.
- Why would you
use untrusted verificaion?
Web Services might use it, as well as non-Windows applications.
- What does the
parameter Initial Catalog define inside Connection String?
The database name to connect to.
- What’s the
data provider name to connect to Access database?
Microsoft.Access.
- What does Dispose
method do with the connection object?
Deletes it from the memory.
- 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.
Rating: 4.00