面试题2：实现Singleton模式

来源：互联网发布：ipad windows 编辑：程序博客网时间：2024/05/17 22:28

题目：设计一个类，我们只能生成该类的一个实例。

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只能生成一个实例的类是实现Singleton（单例）模式的类型。由于设计模式在面向对象程序设计中起着举足轻重的作用，面试中经常会出现这样的面试题。

不好得解决方法一：只适用于单线程环境

public sealed class Singleton{private singleton(){}private static Singleton instance = null;public static Singleton Instance{get{if (instance == null)instance = new Singleton();return instance;}}}

不好的解法二：虽然在多线程环境中能工作但是工作效率不高

public sealed class Singleton{private singleton(){}private static readonly object syncObj = new object();private static Singleton instance = null;public static Singleton Instance{get{lock(syncObj){if (instance == null)instance = new Singleton();}return instance;}}}

可行的解法：加同步锁前后两次判断实例是否已存在

public sealed class Singleton{private singleton(){}private static readonly object syncObj = new object();private static Singleton instance = null;public static Singleton Instance{get{if (instance == null)lock(syncObj){instance = new Singleton();}}return instance;}}

推荐的解法一：利用静态构造函数

public sealed class Singleton{private singleton(){}private static Singleton instance = new Singleton();public static Singleton Instance{get{return instance;}}}

推荐的解法二：实现按需创建实例

public sealed class Singleton{private singleton(){}public static Singleton Instance{get{return instance;}}class Nested{static Nested(){}insternal static readonly Singleton instance = new Singleton();}}

请阅读这篇博客。博主详细讲解了23种设计模式。

转载请注明出处：http://blog.csdn.net/lvsaixia/article/details/39583193

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