Singleton实现

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单例模式的实现大致有以下几种方式：

饿汉式：

/**  * @desc: 饿汉式，类加载时即创建实例  * @desc: feature:可以通过反射机制攻击；线程安全(多个类加载器除外)  * @author: houkh  * @date： Dec 2, 2014  */public class HungrySingletonOfBasic {       public static final HungrySingletonOfBasicinstance = new HungrySingletonOfBasic();       private HungrySingletonOfBasic() {      }}

饿汉式变种1：

/**  * @desc：饿汉式变种  * @author: houkh  * @date： Dec 2, 2014  */public class HungrySingletonTwo {       private static HungrySingletonTwo instance =  new HungrySingletonTwo();       public static HungrySingletonTwo getInstance() {             return instance ;      }       private HungrySingletonTwo() {      }}

饿汉式变种2：

/**  * @desc: 饿汉式变种2，类加载时实例化  * @deprecated something may be wrong  * @author: houkh  * @date： Dec 2, 2014  */public class HungrySingletonThree {       private static HungrySingletonThree instance  = null;       static {             instance = new HungrySingletonThree();      }       private HungrySingletonThree() {      }       public static HungrySingletonThreegetInstance() {             return instance ;      }}

懒汉式：

/**  * @desc: 懒汉式，基本类型  * @desc: feature:延时加载；线程不安全，多线程下不能正常工作；需要额外的serializable/transient/readResolve来实现序列化  * @author: houkh  * @date： Dec 2, 2014  */public class LazySingletonOfBasic {       private static LazySingletonOfBasic instance = null ;       private LazySingletonOfBasic() {      }       public static LazySingletonOfBasic getInstance() {             if (instance == null) {                   instance = newLazySingletonOfBasic();            }             return instance ;      }}

懒汉式变种：

/**  * @desc: 线程安全，效率较低  * @author: houkh  * @date： Dec 2, 2014  */public class LazySingletonTwo {       private static LazySingletonTwo instance =null ;       private LazySingletonTwo() {      }       public static synchronized LazySingletonTwo getInstance() {             if (instance == null) {                   instance = newLazySingletonTwo();            }             return instance ;      }}

静态内部类：

/**  * @desc: 静态内部类：线程安全，延迟加载  * @author: houkh  * @date： Dec 2, 2014  */public class InnerStaticSingleton {       private static class SingletonHolder {             private static final InnerStaticSingleton instance = newInnerStaticSingleton();      }       public static final InnerStaticSingletongetInstance() {             return SingletonHolder. instance;      }       private InnerStaticSingleton() {      }}

双重校验锁：

/**  * @desc：双重校验  * @author: houkh  * @date： Dec 2, 2014  */public class DoubleCheckSingleton {       private volatile static DoubleCheckSingleton  instance;       private DoubleCheckSingleton() {      }       public static DoubleCheckSingleton getInstance() {             if (instance == null) {                   synchronized(DoubleCheckSingleton. class) {                         if (instance == null) {                               instance = newDoubleCheckSingleton();                        }                  }            }             return instance ;      }}

枚举类型：

/**  * @desc: 提供序列化机制，绝对防止多次实例化，即使在面对复杂序列化或反射攻击的时候  * @author: houkh  * @date： Dec 2, 2014  */public enum EnumSingleton {       instance ;}

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