＜细节向＞jdk1.8中HashMap底层链表转红黑树的阈值为什么是8？红黑树转链表为什么是6？

/* * Implementation notes. * * This map usually acts as a binned (bucketed) hash table, but * when bins get too large, they are transformed into bins of * TreeNodes, each structured similarly to those in * . Most methods try to use normal bins, but * relay to TreeNode methods when applicable (simply by checking * instanceof a node). Bins of TreeNodes may be traversed and * used like any others, but additionally support faster lookup * when overpopulated. However, since the vast majority of bins in * normal use are not overpopulated, checking for existence of * tree bins may be delayed in the course of table methods. * * Tree bins (., bins whose elements are all TreeNodes) are * ordered primarily by hashCode, but in the case of ties, if two * elements are of the same "class C implements C