解析C#中的私有构造函数和静态构造函数

class NLog
{
  // Private Constructor:
  private NLog() { }

  public static double e = Math.E; //2.71828...
}

public class Counter
{
  private Counter() { }
  public static int currentCount;
  public static int IncrementCount()
  {
    return ++currentCount;
  }
}

class TestCounter
{
  static void Main()
  {
    // If you uncomment the following statement, it will generate
    // an error because the constructor is inaccessible:
    // Counter aCounter = new Counter();  // Error

    Counter.currentCount = 100;
    Counter.IncrementCount();
    Console.WriteLine("New count: {0}", Counter.currentCount);

    // Keep the console window open in debug mode.
    Console.WriteLine("Press any key to exit.");
    Console.ReadKey();
  }
}

New count: 101

// Counter aCounter = new Counter();  // Error

class SimpleClass
{
  // Static variable that must be initialized at run time.
  static readonly long baseline;

  // Static constructor is called at most one time, before any
  // instance constructor is invoked or member is accessed.
  static SimpleClass()
  {
    baseline = DateTime.Now.Ticks;
  }
}

 public class Bus
 {
   // Static variable used by all Bus instances.
   // Represents the time the first bus of the day starts its route.
   protected static readonly DateTime globalStartTime;

   // Property for the number of each bus.
   protected int RouteNumber { get; set; }

   // Static constructor to initialize the static variable.
   // It is invoked before the first instance constructor is run.
   static Bus()
   {
     globalStartTime = DateTime.Now;

     // The following statement produces the first line of output, 
     // and the line occurs only once.
     Console.WriteLine("Static constructor sets global start time to {0}",
       globalStartTime.ToLongTimeString());
   }

   // Instance constructor.
   public Bus(int routeNum)
   {
     RouteNumber = routeNum;
     Console.WriteLine("Bus #{0} is created.", RouteNumber);
   }

   // Instance method.
   public void Drive()
   {
     TimeSpan elapsedTime = DateTime.Now - globalStartTime;

     // For demonstration purposes we treat milliseconds as minutes to simulate
     // actual bus times. Do not do this in your actual bus schedule program!
     Console.WriteLine("{0} is starting its route {1:N2} minutes after global start time {2}.",
                 this.RouteNumber,
                 elapsedTime.TotalMilliseconds,
                 globalStartTime.ToShortTimeString());
   }
 }

 class TestBus
 {
   static void Main()
   {
     // The creation of this instance activates the static constructor.
     Bus bus1 = new Bus(71);

     // Create a second bus.
     Bus bus2 = new Bus(72);

     // Send bus1 on its way.
     bus1.Drive();

     // Wait for bus2 to warm up.
     System.Threading.Thread.Sleep(25);

     // Send bus2 on its way.
     bus2.Drive();

     // Keep the console window open in debug mode.
     System.Console.WriteLine("Press any key to exit.");
     System.Console.ReadKey();
   }
 }

   Static constructor sets global start time to 3:57:08 PM.
   Bus #71 is created.
   Bus #72 is created.
   71 is starting its route 6.00 minutes after global start time 3:57 PM.
   72 is starting its route 31.00 minutes after global start time 3:57 PM.