An error occurred while debugging eclipse. The class file cannot be compiled.

 Today at the companyProgramDue to time factors, you need to adjust the system time to the previous few years. When the bug is fixed and running, why not report a null pointer error if (Object = NULL, it is true to use the eclipse breakpoint to check the items in if, but then press F6 to report an exception. It is really inexplicable. Later, my colleague reminded me to check the class directory of the project, I found that the modified Java file was not compiled at all. But isn't eclipse automatically compiled? At this time, I found that the modified Java file was generated in because I changed the system time, but the old class file was already in, therefore, eclipse may think that the class file has been compiled, so it will not be re-compiled, change the system time back to the current, save the modification, and everything is OK.