C# interview Questions and Answers

C# interview Questions and Answers :

What is the syntax to inherit from a class in C#?

Place a colon and then the name of the base class. Example: class MyNewClass :

MyBaseClass

Can you prevent your class from being inherited by another class?

Yes. The keyword “sealed” will prevent the class from being inherited.

Can you allow a class to be inherited, but prevent the method from being overridden?

Yes. Just leave the class public and make the method sealed.

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 the class itself is inherited from an abstract class, but not all base abstract

methods have been overridden.

2. When at least one of the methods in the class is abstract.

What is an interface class?

Interfaces, like classes, define a set of properties, methods, and events. But unlike classes,

interfaces do not provide implementation. They are implemented by classes, and defined

as separate entities from classes.

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

They all must be public, and are therefore public by default.

Can you inherit multiple interfaces?

Yes. .NET does support multiple interfaces.

What happens if you inherit multiple interfaces and 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. To Do: Investigate

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

System.Object.

What does the term immutable mean?

The data value may not be changed. Note: The variable value may be changed, but the

original immutable data value was discarded and a new data value was created in

memory.

What’s the difference between System.String and System.Text.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 cases where there is a large amount of string

manipulation. Strings are immutable, so each time a string is changed, a new instance in

memory 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 Clone() method returns a new array (a shallow copy) object containing all the

elements in the original array. The CopyTo() method copies the elements into another

existing array. Both perform a shallow copy. A shallow copy means the contents (each

array element) contains references to the same object as the elements in the original array.

A deep copy (which neither of these methods performs) would create a new instance of

each element's object, resulting in a different, yet identacle object.

How can you sort the elements of the array in descending order?

By calling Sort() and then Reverse() methods.

What’s the .NET collection class that allows an element to be accessed using a

unique key?

HashTable.

What class is underneath the SortedList class?

A sorted HashTable.

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

Yes.

What’s the C# syntax to catch any possible exception?

A catch block that catches the exception of type System.Exception. You can also omit the