java單例

/**

 *五、 雙重校驗鎖

 */

class LockSingleton{

    private volatile static LockSingleton singleton;

    private LockSingleton(){}

     

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

    public static LockSingleton getInstance(){

        if(singleton==null){

            synchronized(LockSingleton.class){

                if(singleton==null){

                    singleton=new LockSingleton();

                }

            }

        }

        return singleton;

    }

     

}

/**

 * 四、枚舉

 */

enum EnumSingleton{

    INSTANCE;

    public void doSomeThing(){

    }

}

/**

 * 三、靜態內部類

 */

class InternalSingleton{

    private static class SingletonHolder{

        private final static  InternalSingleton INSTANCE=new InternalSingleton();

    }  

    private InternalSingleton(){}

    public static InternalSingleton getInstance(){

        return SingletonHolder.INSTANCE;

    }

}

/**

 * 二、惡漢

 */

class HungrySingleton{

    private static HungrySingleton singleton=new HungrySingleton();

    private HungrySingleton(){}

    public static HungrySingleton getInstance(){

        return singleton;

    }

}

/**

 * 一、懶漢

 */

class LazySingleton{

    private static LazySingleton singleton;

    private LazySingleton(){

    }

    public static LazySingleton getInstance(){

        if(singleton==null){

            singleton=new LazySingleton();

        }

        return singleton;

    }