单例用于确保仅创建对象的一个实例。单例仅允许创建其自身的单个实例，这意味着它将控制其创建。单例是“四人帮”设计模式之一，是一种创造模式。
public sealed class Singleton
{
private static Singleton _instance;
private static object _lock = new object();
private Singleton()
{
}
public static Singleton GetSingleton()
{
if (_instance == null)
{
CreateSingleton();
}
return _instance;
}
private static void CreateSingleton()
{
lock (_lock )
{
if (_instance == null)
{
_instance = new Singleton();
}
}
}
}Jon Skeet为惰性，线程安全的单例提供以下实现：
public sealed class Singleton
{
private static readonly Lazy<Singleton> lazy =
new Lazy<Singleton>(() => new Singleton());
public static Singleton Instance { get { return lazy.Value; } }
private Singleton()
{
}
}