单例模式的几种写法

// 饿汉模式
class God
{
    private static God instance = new God();
    private God(){}
    public static God GetInstance
    {
        return instance;
    }
    
}

// 懒汉模式
class God
{
    private static God _godInstance = null;
    private God(){}
    public static God GetInstance()
    {
        if(_godInstance == null)
        {
            _godInstance = new God();
        }
        return _godInstance;
    }
}

// 多线程
class God
{
    private static God _godInstance = null;
    private static object locker = new object();
    private God(){}
    private static God GetInstance()
    {
        if(_godInstance == null)
        {
            lock(locker)
            {
                if(_godInstance == null)
                {
                    _godInstance = new God();
                }
            }
        }
        return _godInstance;
    }
}