单例模式

单例模式也就是保证一个类只有一个实例的一种实现方法，

   class Program
    {
        static void Main(string[] args)
        {
            Earth person = Earth.GetEarth();
            person.Population();
        }
    }
    class Earth
    {
       private static Earth person = new Earth();
       private Earth() { }
       public static Earth GetEarth() 
       {
           return person;
       }
       public string Population();
    }

class Peson
    {
        private Peson() 
        { 
        }

        private static Peson p = new Peson();

        public static Peson Get()
        {
            return p;
        }
    }

class Program
    {
        static void Main(string[] args)
        {
            Peson p = Peson.Get();
        }
    }