http://blog.csdn.net/qq_27093465/article/details/52207135
http://blog.csdn.net/qq_27093465/article/details/52207152
源码
http://hg.openjdk.java.net/jdk6/jdk6/jdk/file/e0220f50a3b4/src/share/classes/java/util/HashMap.java
http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/share/classes/java/util/HashMap.java
