转自：http://www.cnblogs.com/lovebread/archive/2009/11/23/1609122.html
JVM 讲解
http://yuzhouwan.com/2016/07/16/%E5%A6%82%E4%BD%95%E8%BF%90%E7%94%A8JVM%E7%9F%A5%E8%AF%86%E6%8F%90%E9%AB%98%E7%BC%96%E7%A8%8B%E6%B0%B4%E5%B9%B3/