The classes in the Eclipse Project sometimes make a lot of mistakes.

Since the compilation of Eclipse is based on the time stamp judgment mechanism.
So when you press build all, some of the classes that eclipse thinks the timestamp hasn't changed will not be compiled.
So you can clean it and compile it first. At this point eclipse will clean up all the previously compiled information and compile it.
Eclipse--->project----->clean ...
option to delete the. class file in the project while recompiling the project, similar to the rebuild in Jbuild

The classes in the Eclipse Project sometimes make a lot of mistakes.