/// <summary>
  /// 靜態(tài)單例
  /// </summary>
  /// <typeparam name="TClass">單例類型</typeparam>
  public static class Singleton<TClass> where TClass : class, new()
  {
    private static readonly object _lock = new object();
    private static TClass _instance = default(TClass);

    /// <summary>
    /// 獲取單例實例
    /// </summary>
    public static TClass GetInstance()
    {
      return Instance;
    }

    /// <summary>
    /// 單例實例
    /// </summary>
    public static TClass Instance
    {
      get
      {
        if (_instance == null)
        {
          lock (_lock)
          {
            if (_instance == null)
            {
              _instance = new TClass(); // must be public constructor
            }
          }
        }

        return _instance;
      }
    }

    /// <summary>
    /// 設置單例實例
    /// </summary>
    /// <param name="instance">單例實例</param>
    public static void Set(TClass instance)
    {
      lock (_lock)
      {
        _instance = instance;
      }
    }

    /// <summary>
    /// 重置單例實例
    /// </summary>
    public static void Reset()
    {
      lock (_lock)
      {
        _instance = default(TClass);
      }
    }
  }

class Program
  {
    interface IInterfaceA
    {
      string GetData();
    }
    class ClassA : IInterfaceA
    {
      public string GetData()
      {
        return string.Format("This is from ClassA with hash [{0}].", this.GetHashCode());
      }
    }
    static void Main(string[] args)
    {
      string data1 = Singleton<ClassA>.GetInstance().GetData();
      Console.WriteLine(data1);
      string data2 = Singleton<ClassA>.GetInstance().GetData();
      Console.WriteLine(data2);

      Console.ReadKey();
    }
  }