Prior to Java-5 ，编译器竟然会调整语句的顺序来优化！！！
解释链接：
http://www.cs.umd.edu/~pugh/java/memoryModel/jsr-133-faq.html#volatile
解释链接：
http://www.cs.umd.edu/~pugh/java/memoryModel/jsr-133-faq.html#volatile
To see a world in a grain of sand.
And a heaven in a wild flower
Hold infinity in the palm of your hand.
And eternity in an hour
一花一世界
一沙一天堂
掌中握无限
霎那成永恒
