标签：des c style class blog code
单例模式的话，类图上来看是最简单的设计模式，就是一个类只能有一个自己的实例。
单例模式通常来说我们就有Lazy loading的和不是Lazy loading的。《java与模式》里面的关于这两种的类图，：
可以看到一个是现开始就实例话的，这样的话不符合我们的lazy loading,还有一种是在getinstance方法里头去new的，这样的话会有线程安全的问题，我们提供了双重检查锁。
下面看示意代碼︰
1． 静态初始化：
package com.javadesignpattern.Singleton; public class SingletonLazyLoading { private static SingletonLazyLoading instance = new SingletonLazyLoading(); private SingletonLazyLoading(){ } public static SingletonLazyLoading getInstance(){ return instance; } }
2．双重检察锁
package com.javadesignpattern.Singleton; public class SingletonNonLazyLoading { private static volatile SingletonNonLazyLoading instance; private SingletonNonLazyLoading(){ } public static SingletonNonLazyLoading getInstance(){ synchronized(SingletonNonLazyLoading.class){ if(instance == null){ instance = new SingletonNonLazyLoading(); } } return instance; } }
3．静态内部类
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package
com.javadesignpattern.Singleton;public class SingletonStaticInnerClass { private
SingletonStaticInnerClass(){ } static
class InnerClass{ private
static SingletonStaticInnerClass instance = new
SingletonStaticInnerClass(); } public
static SingletonStaticInnerClass getInstance(){ return
InnerClass.instance; }} |
4． 枚举
package com.citi.designpattern.singleton; public class SingletonEnum { public static void main(String[] args){ System.out.println(Singleton.INSTANCE == Singleton.getInstance()); } } enum Singleton { INSTANCE; public static Singleton getInstance(){ return INSTANCE; } }
测试代码：
package com.javadesignpattern.Singleton; public class TestMain { public static void main(String[] args){ //1.LazyLoading /*SingletonLazyLoading singleton1 = SingletonLazyLoading.getInstance(); SingletonLazyLoading singleton2 = SingletonLazyLoading.getInstance(); System.out.println(singleton1 == singleton2);*/ //2.No-LazyLoading SingletonNonLazyLoading instance1 = SingletonNonLazyLoading.getInstance(); SingletonNonLazyLoading instance2 = SingletonNonLazyLoading.getInstance(); System.out.println(instance1 == instance2); //3. static inner class SingletonStaticInnerClass sInstance1 = SingletonStaticInnerClass.getInstance(); SingletonStaticInnerClass sInstance2 = SingletonStaticInnerClass.getInstance(); System.out.println(sInstance1 == sInstance2); //4. Enum System.out.println(Singleton.INSTANCE == Singleton.getInstance()); } } enum Singleton { INSTANCE; public static Singleton getInstance(){ return INSTANCE; } }
枚举的方式始effective java推荐的。序列化的时候能保证单例，而且比较简单。当然别的方式的序列化可以用重写 readreslove 来保证单例。
//readResolve
to prevent another instance of Singleton private Object
readResolve(){ return INSTANCE; }设计模式（四） ： 创建型模式－－单例模式,布布扣,bubuko.com
标签：des c style class blog code
原文地址：http://www.cnblogs.com/ChristyorRuth/p/3759793.html
