1、add configuration时无法识别源代码中的主类，src里的.java文件无法识别为蓝色Class标志
Project Structure -> Modules -> 'Project_Name' -> Sources (tab) -> click src folder -> Mark as: Sources
https://stackoverflow.com/questions/2199711/class-file-not-found-in-intellij
2、对象的部分方法无法识别，cannot access xxx
重启idea好了。。。谜
https://blog.csdn.net/qa275267067/article/details/100512663
3、运行后报错：无效的源发行版:14
修改settings和Project Structure中的language level
https://www.cnblogs.com/chenyanbin/p/12168522.html
