Generics are mainly used when you don't want to specify any passing parameter data type or class return type . It will be decide on run time while invoking the method or class.

Example of Generic class:

using System;
using System.Collections.Generic;

namespace GenericApplication
{
   public class MyGenericArray<T>
   {
      private T[] array;
      public MyGenericArray(int size)
      {
         array = new T[size + 1];
      }

      public T getItem(int index)
      {
         return array[index];
      }

      public void setItem(int index, T value)
      {
         array[index] = value;
      }
   }

   class Tester
   {
      static void Main(string[] args)
      {

         //declaring an int array
         MyGenericArray<int> intArray = new MyGenericArray<int>(5);

         //setting values
         for (int c = 0; c < 5; c++)
         {
            intArray.setItem(c, c*5);
         }

         //retrieving the values
         for (int c = 0; c < 5; c++)
         {
            Console.Write(intArray.getItem(c) + " ");
         }

         Console.WriteLine();

         //declaring a character array
         MyGenericArray<char> charArray = new MyGenericArray<char>(5);

         //setting values
         for (int c = 0; c < 5; c++)
         {
            charArray.setItem(c, (char)(c+97));
         }

         //retrieving the values
         for (int c = 0; c< 5; c++)
         {
            Console.Write(charArray.getItem(c) + " ");
         }
         Console.WriteLine();

         Console.ReadKey();
      }
   }
}

Generic Methods

Previous example was generic class now we will use generic methods

Ex:
using System;
using System.Collections.Generic;

namespace GenericMethodAppl
{
   class Program
   {
      static void Swap<T>(ref T lhs, ref T rhs)
      {
         T temp;
         temp = lhs;
         lhs = rhs;
         rhs = temp;
      }
      static void Main(string[] args)
      {
         int a, b;
         char c, d;
         a = 10;
         b = 20;
         c = 'I';
         d = 'V';

         //display values before swap:
         Console.WriteLine("Int values before calling swap:");
         Console.WriteLine("a = {0}, b = {1}", a, b);
         Console.WriteLine("Char values before calling swap:");
         Console.WriteLine("c = {0}, d = {1}", c, d);

         //call swap
         Swap<int>(ref a, ref b);
         Swap<char>(ref c, ref d);

         //display values after swap:
         Console.WriteLine("Int values after calling swap:");
         Console.WriteLine("a = {0}, b = {1}", a, b);
         Console.WriteLine("Char values after calling swap:");
         Console.WriteLine("c = {0}, d = {1}", c, d);

         Console.ReadKey();
      }
   }
}