求助各位大佬，这样的问题怎样解决？

Exception in thread "main" java.lang.Error: Unresolved compilation problems:
TreeSet cannot be resolved to a type
Peroson cannot be resolved to a type
TreeSet cannot be resolved to a type
Peroson cannot be resolved to a type

还有一个问题是：文件可以运行，但是class为什么会显示×