C# 单例与延迟加载

//这是一个单例，
//调用：A.Instence().Start()
public sealed class A
{
    private static readonly A instence = null;
    static A()
    {
        instence = new A();
    }
    private A()
    {
        //初始化
    }
    public static A Instence()
    {
        return instence;
    }
    public void Start()
    {
        //do something
    }
}

 //延迟加载
 //调用：A.Instance.Start()
 //执行到调用代码的时候才会去创建类的实例对象
public sealed class A
{
    static readonly Lazy<A> instanceHolder = new Lazy<A>(() => new A());     
　　 A()
　　{
　　　　// 初始化
　　}
    public static A Instance => instanceHolder.Value;
    public void Start()
    {
         //do something
    }
}