title: C# and StringBuilder. I am new to C#. I could not understand the output
body: <pre><code>using System;
  using System.Text;
  
  namespace Objects
  {
      class Program
      {
          static void Main(string[] args)
          {
              StringBuilder x = new StringBuilder(), y = x;
              x.Append("Hello, ");
              y.Append("World");
              Console.WriteLine(x.ToString());//prints Hello, World
              Console.WriteLine(y.ToString());//prints Hello, World
              x = null;
              Console.WriteLine(x); // produces NullString
              Console.WriteLine(y.ToString()); //prints Hello, World.How does it print Hello, World
              Console.ReadLine();
  
          }
      }
  }
  </code></pre>