Shallow Size V.S. Retained Size

Shallow vs. Retained Heap
http://help.eclipse.org/mars/index.jsp?topic=%2Forg.eclipse.mat.ui.help%2Fconcepts%2Fshallowretainedheap.html

Java堆：Shallow Size和Retained Size
http://blog.csdn.net/kingzone_2008/article/details/9083327