Map综述：
HashMap详解
https://blog.csdn.net/justloveyou_/article/details/62893086
LinkedHashMap详解：
https://blog.csdn.net/justloveyou_/article/details/71713781
ConcurrentHashMap详解：
https://blog.csdn.net/justloveyou_/article/details/72783008
原文：https://www.cnblogs.com/Jason2018/p/9827401.html