BOXING AND UNBOXING TYPES

BOXING AND UNBOXING TYPES

Boxing refers to converting a value type to an object type, and unboxing refers to the opposite.
Boxing is carried out implicitly in C#, use type casting to unbox to an appropriate data type.

For example
int i; Console.WriteLine("i={0}",i);

The WriteLine() method requires an object, so in the above statement integer i is implicitly boxed to an object and passed to the WriteLine method.

An example for unboxing is
    int i;
    object obj = i;  // boxing is implicit
    int j;
    j = (int) obj; // to unbox we use type cast

Typically unboxing is done in a try block. If the object being unboxed is null or if the unboxing cannot succeed because the object is of a different type, an InvalidCastException is thrown.

DELEGATES
A delegate essentially creates a name for a the specific type/signature of a method. Delegates are type safe function pointers.
One must first declare a delegate.

// delegates.cs
    using System;
// declare delegate with the signature of the  encapsulated method
    delegate void MyDelegate(string m,int a,int b);
    class Application
    {
        public static void Main()
        {
             MyDelegate md = new MyDelegate(FirstMethod);
             md += new MyDelegate(SecondMethod);
            md("message A",4,5);
            md("message B",7,11);
         } // end Main
}

    static void FirstMethod(string s1,int x1,int y1)
    {
         Console.WriteLine("1st method: " + s1);
         int sum1 = x1 + y1;
         Console.WriteLine("sum1 = " + sum1);
    }
   static void SecondMethod(string s2,int x2,int y2)
   {
         Console.WriteLine("2st method: " + s2);
          int sum2 = x2 + y2;
          Console.WriteLine("sum2 = " + sum2);
    }

OUTPUT :

1st method message A
sum1 = 9
2st method message A
sum2 = 9
1st method message B
sum1 = 18
2st method message B
sum2 = 18


TYPES :

The typeof command is an operator. It resolves at compile time and operates over a type. To check whether an object is compatible to a specific type is to apply the is keyword.

// myTypeof.cs
using System;
using System.Text;
class myTypeof
{
    public static void Main()
     {
             double b = 3.14;
             string s = "xxx";
             StringBuilder sb = new StringBuilder("123456789");
    }
        Type at = typeof(double);
        Console.WriteLine("at = {0}",at);
        Type st = typeof(string);
        Console.WriteLine("st = {0}",st);
        Type sbt = typeof(StringBuilder);
        Console.WriteLine("sbt = {0}",sbt);
        if(s is string)    
         {
            Console.WriteLine(at);
          }
          if(s is StringBuilder)    
          {
                Console.Write("s is of the StringBuilder");
           }
            else
            {
                 Console.Write("s is not of StringBuilder");
            }
        if(b is int)
        {
        Console.WriteLine("b is int");
         }
}