JAVA8的java.util.function包
https://www.cnblogs.com/linzhanfly/p/9686941.html
java.util.function.Function的用法
https://www.jianshu.com/p/3c27dfd647f1
https://blog.csdn.net/huo065000/article/details/78964382
java8双冒号用法：
https://www.jianshu.com/p/96b4815d629e