設計模式實例-單例

using System;
using System.Linq;
using System.Text;
namespace Ahoo.Demo.DesignPatterns.Patterns.Singleton
{

    /* ####### 單例模式 #######
     * 保證一個類只有一個實例，
     * 並提供一個全局訪問點
     */
    /// <summary>
    /// 懶漢式單例類
    /// </summary>
    public class Singleton
    {
        /// <summary>
        /// 靜態唯一實例
        /// 第一次調用時初始化
        /// </summary>
        private static Singleton instance;
        /// <summary>
        /// 同步鎖
        /// </summary>
        private static readonly object syncRoot = new object();

        /// <summary>
        /// 私有化構造函數
        /// </summary>
        private Singleton()
        {
        }
        /// <summary>
        /// 雙重鎖，降低鎖機製造成的性能影響
        /// </summary>
        /// <returns></returns>
        public static Singleton GetInstance()
        {
            if (instance == null)
            {
                lock (syncRoot)
                {
                    if (instance == null)
                    {
                        instance = new Singleton();
                    }
                }
            }
            return instance;
        }
    }

    /// <summary>
    /// 惡漢式單例類
    /// </summary>
    public class Singleton2
    {
        /// <summary>
        /// 程序啓動時即初始化實例
        /// </summary>
        private static readonly Singleton2 instance = new Singleton2();

        /// <summary>
        /// 私有化構造函數
        /// </summary>
        private Singleton2()
        {
        }

        public static Singleton2 GetInstance()
        {
            return instance;
        }
    }

    public class Client
    {
        public static void Excute()
        {
            Singleton singleton = Singleton.GetInstance();

            Singleton2 singleton2 = Singleton2.GetInstance();
        }
    }
}