第一种最简单，但没有考虑线程安全，在多线程时可能会出问题，不过俺从没看过出错的现象，表鄙视我……
public class Singleton{ private static Singleton _instance = null; private Singleton(){} public static Singleton CreateInstance() { if(_instance == null)
{ _instance = new Singleton(); } return _instance; }}
第二种考虑了线程安全，不过有点烦，但绝对是正规写法，经典的一叉
public class Singleton{ private volatile static Singleton _instance = null; private static readonly object lockHelper = new object(); private Singleton(){} public static Singleton CreateInstance() { if(_instance == null) { lock(lockHelper) { if(_instance == null) _instance = new Singleton(); } } return _instance; }}第三种可能是C#这样的高级语言特有的，实在懒得出奇
public class Singleton{
private Singleton(){} public static readonly Singleton instance = new Singleton();} 哦，shit！
