java synchronized 详解: http://www.cnblogs.com/devinzhang/archive/2011/12/14/2287675.html
java 单例模式和同步锁synchronize: http://blog.csdn.net/sadfishsc/article/details/8007934
java synchronized 详解: http://www.cnblogs.com/devinzhang/archive/2011/12/14/2287675.html
java 单例模式和同步锁synchronize: http://blog.csdn.net/sadfishsc/article/details/8007934