java单例

/**

 *五、 双重校验锁

 */

classLockSingleton{

    privatevolatile static LockSingleton singleton;

    privateLockSingleton(){}

     

    //详见：http://www.ibm.com/developerworks/cn/java/j-dcl.html

    publicstatic LockSingleton getInstance(){

        if(singleton==null){

            synchronized(LockSingleton.class){

                if(singleton==null){

                    singleton=newLockSingleton();

                }

            }

        }

        returnsingleton;

    }

     

}

/**

 * 四、枚举

 */

enumEnumSingleton{

    INSTANCE;

    publicvoid doSomeThing(){

    }

}

/**

 * 三、静态内部类

 */

classInternalSingleton{

    privatestatic class SingletonHolder{

        privatefinal static  InternalSingleton INSTANCE=newInternalSingleton();

    }  

    privateInternalSingleton(){}

    publicstatic InternalSingleton getInstance(){

        returnSingletonHolder.INSTANCE;

    }

}

/**

 * 二、恶汉

 */

classHungrySingleton{

    privatestatic HungrySingleton singleton=newHungrySingleton();

    privateHungrySingleton(){}

    publicstatic HungrySingleton getInstance(){

        returnsingleton;

    }

}

/**

 * 一、懒汉

 */

classLazySingleton{

    privatestatic LazySingleton singleton;

    privateLazySingleton(){

    }

    publicstatic LazySingleton getInstance(){

        if(singleton==null){

            singleton=newLazySingleton();

        }

        returnsingleton;

    }