Nested Class Problem in C#

Question

Hi
i have make a program in which two nested classes one is outer class and other is inner class and just i have make their just constructor and i inherit them with the main class demo when ever i make an object of demo class by default outer class constructor is calling can any one tell me why it is calling although i am not making outer class object why it is calling....................? w8ing for rep

class demo :outerClass

{

static void Main(string[] arg)

{

demo d = new demo();

}

class outerClass

{

public outerClass()

{

Console.WriteLine ("This is outer constructor");

}

class innerClass

{

public innerClass()

{

Console.WriteLine("This is inner class constructor");

}

Anuja Pawar · Answer

Hi Your Demo Class does not have its own constructor  so it uses the outerclass constructor and you can see the results  This is outer constructor  So Try this class demo : outerClass { public demo(): base(From derived) { Console.WriteLine(This is demo constructor); Console.ReadKey(); } static void Main(string[] arg) { demo d = new demo(); } } class outerClass { public outerClass() { Console.WriteLine(This is outer constructor); Console.ReadKey(); } public outerClass(string a) { Console.WriteLine(a); } class innerClass { public innerClass() { Console.WriteLine(This is inner class constructor); Console.ReadKey(); } } } For more details read this http://www.csharp-station.com/Tutorials/lesson08.aspx

Anuja Pawar · Answer

try this as in ur parent class you are saying it has a string parameter so u have to pass a string. Hope you understand the concept. Good luck class parent { public parent(string a) { Console.WriteLine(a + parent class constructor); } } class child : parent { public child():base(test) { Console.WriteLine(Child constructor); } } class MaIn : child { static void Main(string[] arg) { //MaIn obj = new MaIn(this is main cons); parent p = new parent(adfadsfa); } }

Vulpes · Answer

The problem is that child's constructor is looking for a parameterless parent constructor to call but there isn't one. The only constructor is has takes a string argument. You can avoid the error by making the highlighted alteration: class child : parent { public child() : base(Calling from Child constructor the ) { Console.WriteLine(Child constructor); } }

Smart Lucky · Answer

Hi i have write this program it is not running it is giving me error can any one tell me how can i do this................? using System; class parent { public parent(string a) { Console.WriteLine(a + parent class constructor); } } class child : parent { public child() { Console.WriteLine(Child constructor); } } class MaIn : child { static void Main(string[] arg) { //MaIn obj = new MaIn(this is main cons); parent p = new parent(adfadsfa); } }

Vulpes · Answer

Whenever you call any constructor in C# the first thing that happens is that it calls its base class constructor. That in turn calls its base class constructor and so on up to System.Object's constructor. This is necessary to ensure that any members inherited from the ancestor classes are initialized by their respective constructors. In the case of a constructor such as this (or the default constructor if you don't supply one yourself): public demo() { // code if non-default constructor } it is compiled as though it was written like this i.e. the base class's parameterless constructor is called: public demo() : base() { // code if non-default constructor } However you can also explicitly specify that a base class constructor which takes parameters should be called as in Anuja's example: public demo(): base(From derived) { // code }

Vulpes · Answer

Even if the demo class did have a non-default constructor it would still call its base class constructor before any of the code in the demo constructor executes. For example this version of the program: using System; class demo :outerClass { static void Main(string[] arg) { demo d = new demo(); } public demo() { Console.WriteLine(This is demo constructor); } } class outerClass { public outerClass() { Console.WriteLine (This is outer constructor); new innerClass(); } class innerClass { public innerClass() { Console.WriteLine(This is inner class constructor); } } } produces the following output: This is outer constructor This is inner class constructor This is demo constructor