设计模式读书笔记-单件模式（创建型模式）

1     public class SingletonTest
2     {
3         public static readonly SingletonTest Instance = new SingletonTest();
4         private SingletonTest() { }
5     }

1     public class SingletonTest
2     {
3         public static readonly SingletonTest Instance;
4         static SingletonTest()
5         {
6             Instance = new SingletonTest();
7         }
8         private SingletonTest() { }
9     }

 1     public class SingletonTest
 2     {
 3         private static volatile SingletonTest instance = null;
 4         private static object lockobj = new object();
 5         private SingletonTest() { }
 6         public static SingletonTest Instance
 7         {
 8             get
 9             {
10                 if (instance == null)
11                 {
12                     lock (lockobj)
13                     {
14                         if (instance == null)
15                         {
16                             instance = new SingletonTest();
17                         }
18                     }
19                 }
20                 return instance;
21             }
22         }
23     }