General Questions 1.Does C# support multiple-inheritance? No. But you can use Interfaces. 2.Where is a protected class-level variable available? It is available to any sub-class derived from base class 3.Are private class-level variables inherited? Yes, but they are not accessible. 4.Describe the accessibility modifier “protected internal”. It is available to classes that are within the same assembly and derived from the specified base class. 6.Which class is at the top of .NET class hierarchy? System.Object. 7.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. 8.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. 9.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. 10.Can you store multiple data types in System.Array? No. 11.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. 12.How can you sort the elements of the array in descending order? By calling Sort() and then Reverse() methods. 13.What’s the .NET collection class that allows an element to be accessed using a unique key? HashTable. 14.What class is underneath the SortedList class? A sorted HashTable. 15.Will the finally block get executed if an exception has not occurred? Yes. 16.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 parameter data type in this case and just write catch {}. 17.Can multiple catch blocks be executed for a single try statement? No. Once the proper catch block processed, control is transferred to the finally block . 18.Explain the three services model commonly know as a three-tier application? Presentation (UI), Business (logic and underlying code) and Data (from storage or other sources). Class Questions 1.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 2.Can you prevent your class from being inherited by another class? Yes. The keyword “sealed” will prevent the class from being inherited. 3.Can you allow a class to be inherited, but prevent the method from being over-ridden? Yes. Just leave the class public and make the method sealed. 4.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. 5.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. 6.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. 7.Why can’t you specify the accessibility modifier for methods inside the interface? They all must be public, and are therefore public by default. 8.Can you inherit multiple interfaces? Yes. .NET does support multiple interfaces. 9.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. 10. What’s the difference between an interface and abstract class? In an interface class, all methods are abstract - there is no implementation. In an abstract class some methods can be concrete. In an interface class, no accessibility modifiers are allowed. An abstract class may have accessibility modifiers. 11. What is the difference between a Struct and a Class? Structs are value-type variables and are thus saved on the stack, additional overhead but faster retrieval. Another difference is that structs cannot inherit. Method and Property Questions 1. What’s the implicit name of the parameter that gets passed into the set method/property of a class? Value. The data type of the value parameter is defined by whatever data type the property is declared . 2. What does the keyword “virtual” declare for a method or property? The method or property can be overridden. 3. 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. 4. Can you declare an override method to be static if the original method is not static? No. The signature of the virtual method must remain the same. (Note: Only the keyword virtual is changed to keyword override) 5. What are the different ways a method can be overloaded? Different parameter data types, different number of parameters, different order of parameters. 6. If a base class has a number of overloaded constructors, and an inheriting class has a number of overloaded constructors; can you enforce a call from an inherited constructor to a specific 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. Events and Delegates 1. What’s a delegate? A delegate object encapsulates a reference to a method. 2. What’s a multicast delegate? A delegate that has multiple handlers assigned to it. Each assigned handler (method) is called. 3. 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. 4. How do you inherit from a class in C#? Place a colon and then the name of the base class. 5. Does C# support multiple inheritance? No, use interfaces instead. 6. When you inherit a protected class-level variable, who is it available to? Classes in the same namespace. 7. 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. 8. 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). 9. 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. 10. What’s the top .NET class that everything is derived from? System.Object. 11. 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. 12. What does the keyword virtual mean in the method definition? The method can be over-ridden. 13. 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. 14. 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. 15. 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. 16. 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. 17. 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. 18. 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. 19. What’s an interface class? It’s an abstract class with public abstract methods all of which must be implemented in the inherited classes. 20. 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. 21. Can you inherit multiple interfaces? Yes, why not. 22. 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. 23. 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. 24. How can you overload a method? Different parameter data types, different number of parameters, different order of parameters. 25. 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. 26. 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. 27. Is it namespace class or class namespace? The .NET class library is organized into namespaces. Each namespace contains a functionally related group of classes so natural namespace comes first.
To who this may concern, Who and when were you given permission to post my book on the internet, Little men on the radio. There is a revolving clock with a revolving date on your site with my book. That was before you reduced the size of explosing my book for free. If it wasn't for sneaky lying people and organizations such as yourselves and all who hide behind the internet, I never would of had to write the book in the first place. I want to see a copy of my permission to post my book on your site. Thank you. Sincerely, Sophia Schessler
thanks Alot.so informative Question.plz tell me 1 thing. what is difference between mutable and immutable?
Hi everybody, I uploaded one file. But It can not display. I used internet explorer 8.0. How can I repair? Or some problems happened to IE8? Rgs
Interesting interview questions. It helped me remember all the answers. Thanks a lot. Would like to see some .NET 3.0 or 4.0 questions too.
Actually, Protected Internal can be accessed by any code in the assembly in which it is declared, or from within a derived class in another assembly. Access from another assembly must take place within a class declaration that derives from the class in which the protected internal element is declared, and it must take place through an instance of the derived class type.
While strictly true, the answer to that question is incorrect. There is nothing stopping you from declaring an array of objects, then populating it with a variety of different data types. For example, the following is perfectly legal: Code: [SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]object[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][] array = [/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]new [/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]object[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][] { 1, [/SIZE][SIZE=2][COLOR=#a31515][SIZE=2][COLOR=#a31515]"abc"[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2], [/SIZE][SIZE=2][COLOR=#0000ff][SIZE=2][COLOR=#0000ff]new [/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2][COLOR=#2b91af][SIZE=2][COLOR=#2b91af]Random[/COLOR][/SIZE][/COLOR][/SIZE][SIZE=2]() };[/SIZE] Of course, that's extremely bad practice, but the fact remains that you can do it.
Class question "Can you allow a class to be inherited, but prevent the method from being over-ridden?" answer (Yes. Just leave the class public and make the method sealed.) is wrong. You cannot use the "sealed" modifier in a public class that is not over-riding the class that implements the method or property that you want to seal. If you want to stop someone from over-riding a method or property just do not add the "virtual" modifier to it The following will raise an error. If you switched the GetPerson in the Person class to include the "virtual" modifier then it would work. public class Person{ public string GetPerson(){ } } public class Member: Person{ override public string GetPerson(){ } }
Mutable Objects: When you have a reference to an instance of an object, the contents of that instance can be altered Immutable Objects: When you have a reference to an instance of an object, the contents of that instance cannot be altered
Hieverybody, Likethe_nell_87, I think the answer in 10th question is not ok (Can you storemultiple data types in System.Array?). If you havea this hierarchy: class Person {}; class Male : Person {}; class Female : Person {}; each Maleor Female object is also a Person object. With an ArrayListobject, I can insert multiple types of the same hierarchy, and then convert theArrayList to an Array using the base type of Person. The following code works fine: Code: class Person { } class Male : Person { } class Female : Person { } class Program { static void Main(string[] args) { ArrayList al = newArrayList(); al.Add(new Female()); al.Add(new Male()); Person auxp = new Person(); al.Add(auxp); Array a = al.ToArray(auxp.GetType()); foreach (Person p in a) { Console.WriteLine(p.GetType().ToString()); } } } So, in myopinion the answer is yes.
