个人理解的单例模式

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication6
{
  public  sealed class Singleton
    {
      static Singleton instance;
      /// <summary>
      /// 为了避免实例不唯一，构造方法私有化
      /// </summary>
      private Singleton() { }
      public static Singleton Instance 
      {
          get 
          {
              return instance == null ? new Singleton() : instance;
          }
      }
      public void dd(){
          Console.WriteLine("fdd");
          Console.ReadLine();
      }
     
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication6
{
    class Program
    {
        static void Main(string[] args)
        {
            Singleton.Instance.dd();
          
            
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication6
{
    public sealed class Singleton
    {
        static Singleton instance;
        static readonly object padlock = new object();
      
        public Singleton() { }
        public static Singleton Instance
        {

            get
            {
                if (instance == null)
                {
                    lock (padlock)
                    {
                        if (instance == null) 
                        {
                            instance=new Singleton() ;
                        }
                        
                    }
                   
                }
                return instance;
            }
        }
        public void dd()
        {
            Console.WriteLine("fdd");
            Console.ReadLine();
        }

    }
}