Java堆栈和引用问题

详见文章：
https://www.cnblogs.com/LeonNew/p/5314731.html
https://www.cnblogs.com/happyPawpaw/p/4443323.html
http://blog.csdn.net/lk274857347/article/details/77512555
http://blog.csdn.net/liu_yujie2011com/article/details/52354238
http://blog.csdn.net/zhouqixiang/article/details/1917071