35. What is the difference between shadow and override?


When you define a class that inherits from a base class, you sometimes want to redefine one or more of the base class elements in the derived class. Shadowing and overriding are both available for this purpose.

Comparison

It is easy to confuse shadowing with overriding. Both are used when a derived class inherits from a base class, and both redefine one declared element with another. But there are significant differences between the two.The following table compares shadowing with overriding.

Point of comparison Shadowing OverridingPurposeShadowing

Protecting against a subsequent base class modification that introduces a member you have already defined in your derived classAchieving polymorphism by defining a different implementation of a procedure or property with the same calling sequence1Redefined elementShadowing

Any declared element typeOnly a procedure (Function, Sub, or Operator) or propertyRedefining elementShadowing

Any declared element typeOnly a procedure or property with the identical calling sequence1Access level of redefining elementShadowing

Any access levelCannot change access level of overridden elementReadability and writability of redefining elementShadowing

Any combinationCannot change readability or writability of overridden propertyControl over redefiningShadowing

Base class element cannot enforce or prohibit shadowingBase class element can specify MustOverride, NotOverridable, or OverridableKeyword usageShadowing

Shadows recommended in derived class; Shadows assumed if neither Shadows nor Overrides specified2Overridable or MustOverride required in base class; Overrides required in derived classInheritance of redefining element by classes deriving from your derived classShadowing

Shadowing element inherited by further derived classes; shadowed element still hidden3Overriding element inherited by further derived classes; overridden element still overridden

1 The calling sequence consists of the element type (Function, Sub, Operator, or Property), name, parameter list, and return type. You cannot override a procedure with a property, or the other way around. You cannot override one kind of procedure (Function, Sub, or Operator) with another kind.

2 If you do not specify either Shadows or Overrides, the compiler issues a warning message to help you be sure which kind of redefinition you want to use. If you ignore the warning, the shadowing mechanism is used.

3 If the shadowing element is inaccessible in a further derived class, shadowing is not inherited. For example, if you declare the shadowing element as Private, a class deriving from your derived class inherits the original element instead of the shadowing element.


36. Should I make my destructor virtual?


A C# destructor is really just an override of the System.Object Finalize method, and so is virtual by definition


37. 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.


38. Are C# constructors the same as C++ constructors?


Very similar, but there are some significant differences. First, C# supports constructor chaining. This means one constructor can call another:class Person

{

public Person( string name, int age ) { … }

public Person( string name ) : this( name, 0 ) {}

public Person() : this( “”, 0 ) {}

}

Another difference is that virtual method calls within a constructor are routed to the most derived implementationError handling is also somewhat different. If an exception occurs during construction of a C# object, the destuctor (finalizer) will still be called. This is unlike C++ where the destructor is not called if construction is not completed.Finally, C# has static constructors. The static constructor for a class runs before the first instance of the class is created.Also note that (like C++) some C# developers prefer the factory method pattern over constructors.


39. Can you declare a C++ type destructor in C# like ~MyClass()?


Yes, but what’s the point, since it will call Finalize(), and Finalize() has no guarantees when the memory will be cleaned up, plus, it introduces additional load on the garbage collector. The only time the finalizer should be implemented, is when you’re dealing with unmanaged code.


40. What are the fundamental differences between value types and reference types?


C# divides types into two categories – value types and reference types. Most of the intrinsic types (e.g. int, char) are value types. Structs are also value types. Reference types include classes, arrays and strings. The basic idea is straightforward – an instance of a value type represents the actual data, whereas an instance of a reference type represents a pointer or reference to the data.The most confusing aspect of this for C++ developers is that C# has predetermined which types are represented as values, and which are represented as references. A C++ developer expects to take responsibility for this decision.For example, in C++ we can do this:int x1 = 3; // x1 is a value on the stack

int *x2 = new int(3) // x2 is a pointer to a value on the heapbut in C# there is no control:int x1 = 3; // x1 is a value on the stack

int x2 = new int();

x2 = 3; // x2 is also a value on the stack!


41.How do you handle errors in VB.NET and C#?


C# and VB.NET use structured error handling (unlike VB6 and earlier versions where error handling was implemented using Goto statement). Error handling in both VB.NET and C# is implemented using Try..Catch..Finally construct (C# uses lower case construct – try…catch…finally).


42. What is the purpose of the finally block?


The code in finally block is guaranteed to run, irrespective of whether an error occurs or not. Critical portions of code, for example release of file handles or database connections, should be placed in the finally block.


43. Can I use exceptions in C#?


Yes, in fact exceptions are the recommended error-handling mechanism in C# (and in .NET in general). Most of the .NET framework classes use exceptions to signal errors.


44. 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.


45. 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 {}


46. How to declare a two-dimensional array in C#?


Syntax for Two Dimensional Array in C Sharp is int[,] ArrayName;


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


Using Array.Sort() and Array.Reverse() methods.int[] arr = new int[3];

arr[0] = 4;

arr[1] = 1;

arr[2] = 5;

Array.Sort(arr);

Array.Reverse(arr);


48. 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.


49. Structs are largely redundant in C++.Why does C# have them?


In C++, a struct and a class are pretty much the same thing. The only difference is the default visibility level (public for structs, private for classes). However, in C# structs and classes are very different. In C#, structs are value types (instances stored directly on the stack, or inline within heap-based objects), whereas classes are reference types (instances stored on the heap, accessed indirectly via a reference). Also structs cannot inherit from structs or classes, though they can implement interfaces. Structs cannot have destructors. A C# struct is much more like a C struct than a C++ struct.


50. How does one compare strings in C#?


In the past, you had to call .ToString() on the strings when using the == or != operators to compare the strings’ values. That will still work, but the C# compiler now automatically compares the values instead of the references when the == or != operators are used on string types. If you actually do want to compare references, it can be done as follows: if ((object) str1 == (object) str2) { … } Here’s an example showing how string compares work:using System;

public class StringTest

{

public static void Main(string[] args)

{

Object nullObj = null; Object realObj = new StringTest();

int i = 10;

Console.WriteLine(\”Null Object is [\” + nullObj + \”]\n\”

+ \”Real Object is [\” + realObj + \”]\n\”

+ \”i is [\” + i + \”]\n\”);

// Show string equality operators

string str1 = \”foo\”;

string str2 = \”bar\”;

string str3 = \”bar\”;

Console.WriteLine(\”{0} == {1} ? {2}\”, str1, str2, str1 == str2 );

Console.WriteLine(\”{0} == {1} ? {2}\”, str2, str3, str2 == str3 );

}

}Output:Null Object is []

Real Object is [StringTest]

i is [10]

foo == bar ? False

bar == bar ? True


51. Where we can use DLL made in C#.Net?


Supporting .Net, because DLL made in C#.Net semi compiled version. It’s not a com object. It is used only in .Net Framework As it is to be compiled at runtime to byte code.


52. If A.equals(B) is true then A.getHashcode & B.gethashcode must always return same hash code.


The answer is False because it is given that A.equals(B) returns true i.e. objects are equal and now its hashCode is asked which is always independent of the fact that whether objects are equal or not. So, GetHashCode for both of the objects returns different value.


53.Is it possible to debug the classes written in other .Net languages in a C# project?


It is definitely possible to debug other .Net languages code in a C# project. As everyone knows .net can combine code written in several .net languages into one single assembly. Same is true with debugging.


54. Does C# has its own class library?


Not exactly. The .NET Framework has a comprehensive class library, which C# can make use of. C# does not have its own class library.


55. IS it possible to have different access modifiers on the get/set methods of a property?


No. The access modifier on a property applies to both its get and set accessors. What you need to do if you want them to be different is make the property read-only (by only providing a get accessor) and create a private/internal set method that is separate from the property.


56. Is it possible to restrict the scope of a field/method of a class to the classes in the same namespace?


There is no way to restrict to a namespace. Namespaces are never units of protection. But if you’re using assemblies, you can use the ‘internal’ access modifier to restrict access to only within the assembly.


57. Is there an equivalent of exit() or quiting 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.


58. What optimization does the C# compiler perform when you use the /optimize+compiler option?

The following is a response from a developer on the C# compiler team: We get rid of unused locals (i.e., locals that are never read, even if assigned). We get rid of unreachable code. We get rid of try-catch with an empty try. We get rid of try-finally with an empty try. We get rid of try-finally with an empty finally. We optimize branches over branches: gotoif A, lab1 goto lab2: lab1: turns into: gotoif !A, lab2 lab1: We optimize branches to ret, branches to next instruction, and branches to branches.