C# 中的Singleton模式

一般写Singleton基本都是一下这个套路

class Singleton 
{
	public static Singleton  instance;

	private Singleton()
	{
	
	}

	public static Singleton Getinstance()
	{
		if(instatnce == null)
		{
			instance = new Singleton();
		}

		return instance;
	}
}

但是今天学到一个C#独有的Singleton写法：

class sealed Singleton 
{
	public static readonly Singleton  instance = new Singleton();

	private Singleton()
	{

	}
}

这种写法简单实用，大大减少了代码量。

但是缺点就是无法被继承，并且启动时就被初始化，无法延迟初始化。

我以这种写法，写了一个简单的LoadBalance类。

public sealed class LoadBalancer
{
    public static readonly LoadBalancer balancer = new LoadBalancer();
    private ArrayList servers = new ArrayList();
    private Random random = new Random();

    protected LoadBalancer() 
    {
        servers.Add("SERVER I");
        servers.Add("SERVER II");
        servers.Add("SERVER III");
        servers.Add("SERVER IV");
        servers.Add("SERVER V");
    }

    public string Server 
    {
        get 
        {
            int i = random.Next(servers.Count);
            return servers[i].ToString();
        }
    }
}

class Program
{
    static void Main(string[] args)
    {
        LoadBalancer b1 = LoadBalancer.balancer;
        LoadBalancer b2 = LoadBalancer.balancer;
        LoadBalancer b3 = LoadBalancer.balancer;
        LoadBalancer b4 = LoadBalancer.balancer;

        if (b1 == b2 || b2 == b3 || b3 == b4)
            Console.WriteLine("Same instance");
        Console.WriteLine(b1.Server);
        Console.WriteLine(b2.Server);
        Console.WriteLine(b3.Server);
        Console.WriteLine(b4.Server);

        Console.ReadLine();
    }
}

调用的结果是：

Same instance

SERVER III

SERVER I

SERVER IV

SERVER IV