C#设计模式随书源代码.全书一共介绍了23种设计模式

				using System;
				
				namespace singleSpooler
				{
					/// 
					/// Summary description for Class1.
					/// 
					public class singleSpooler 	{
						static void Main(string[] args) { 
							Spooler pr1, pr2;
				      //open one printer--this should always work
				      Console.WriteLine ("Opening one spooler");
				      try {
						pr1 = new Spooler();
				      }
				      catch (SingletonException e)	{
						  Console.WriteLine (e.Message);
					  }
				      //try to open another printer --should fail
				      Console.WriteLine ("Opening two spoolers");
				      try{
					      pr2 = new Spooler();
				      }
				      catch (SingletonException e) {
						  Console.WriteLine (e.Message);
					  }
				}
					}
				}