JavaSE --- explicit lock

1 Overview

　　　　1.1, before jdk5 , for  regulating access to shared objects mechanism   only the synchronized , volatile ;

　　　　　　    After jdk5 , provides a  display lock : Lock , ReentrantLock ...;

　　　　　　　　Explicit locks  are not   an alternative internal mechanism of the lock , but   when the inner lock proved to be limited, provide a selectable advanced features ;

　　　　1.2、