Constructors

1.what is a Constructor ?
   Constructor is a method that is called when an instance of an object is created.
   They have the same name as a class.
    eg-
        class Test
       {
             public Test()
            {
            }
        }

2.Can a constructor have access modifier ?
    Yes .The foll are access modifiers allowed -
     1.Public --This is called whenever a class is initialized.
     2.Private- This will prevent the class from being instantiated(creating objects)
     3.Protected-
     4.Internal--cannot be instantiated outside the assembly.

3.If a class has parametrized constructor  do we need to have default constructor?
   c# provides a default constructor with no parameters if there are no explicit ones. But if we
   have a parameterized constructor we need to specify a defualt one with no parameters.

4.what is static constructor?
    

5.Can constructors  be inherited ?
    No.

6.How can you call a base class constructor from a child class ?
   Child class can call base class constructor by using the keyword base.


  

7.In which order  constructor is called in inheritance ?
    If Class B inherits Class A ,when you create object of Class B then Class B contructor is called first then Class A construcotr is called.
  eg-
      class ClassA
{
    public ClassA()
    {
        Console.WriteLine("i am class A");
    }
}

class ClassB:ClassA
{
    public ClassB()
    {
        Console.WriteLine("i am class B");
    }
}

output- i am class B
              i am class A

8.What is Copy  construtor . Do you have this in C#?
 c# does not provide copy constructor.
9.Can constructors be overloaded ?
      Yes.

10.How do you overload a constructor?    
      Overload a constructor by specifying diff parameters.
eg-
            class numbers
           {
                public numbers() {
                 }

               public numbers(int a){
              }
          }
11.How do you call one constructor from another in the same class ?
      By using this keyword. eg-
      class numbers
      {
                public numbers() {
                 }

               public numbers(int a):this(){
              }
       }


12.When you create an object of the above class which constructor is called 
      first ?
      When you instantiate the above class first overloaded constructor is called and then the
       default one is called.


13.Can a constructor call itself by using this keyword ?
      N0 it will through an compile time error.

    
12.Does memory gets allocated when constructor is called ?
       Yes using new operator.


13. what happens when you instantiate an object ?
      When you create instance of  a class using new operator foll happens-
       New memory is allocated
       instance is created on heap
       reference is created on stack and passed on the the instantiated object.


14.What happens if "new" keyword fails while instantiating ?
       it throws OutOfMemoryException.

14.What is default access modifier of constructor ?
       Private


15.Is it Ok to throw an exception from a constructor ?
      No its not preferred. Constructors are used mainly for initialization purpose.but there are
      certain .Net Framewrok classes like DateTime,FileStream et which throw exception from
      constructor.