设计模式实例-单例

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

    /* ####### 单例模式 ####### * 保证一个类只有一个实例， * 并提供一个全局访问点 */
    /// <summary>
    /// 懒汉式单例类
    /// </summary>
    public class Singleton
    {
        /// <summary>
        /// 静态唯一实例
        /// 第一次调用时初始化
        /// </summary>
        private static Singleton instance;
        /// <summary>
        /// 同步锁
        /// </summary>
        private static readonly object syncRoot = new object();

        /// <summary>
        /// 私有化构造函数
        /// </summary>
        private Singleton()
        {
        }
        /// <summary>
        /// 双重锁，降低锁机制造成的性能影响
        /// </summary>
        /// <returns></returns>
        public static Singleton GetInstance()
        {
            if (instance == null)
            {
                lock (syncRoot)
                {
                    if (instance == null)
                    {
                        instance = new Singleton();
                    }
                }
            }
            return instance;
        }
    }

    /// <summary>
    /// 恶汉式单例类
    /// </summary>
    public class Singleton2
    {
        /// <summary>
        /// 程序启动时即初始化实例
        /// </summary>
        private static readonly Singleton2 instance = new Singleton2();

        /// <summary>
        /// 私有化构造函数
        /// </summary>
        private Singleton2()
        {
        }

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

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

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