How to solve the issue of not finding classes when compiling a multi-module project in IntelliJ IDEA?

In a multi-module project, there are several possible solutions to try when a class cannot be found during compilation.

1. Check dependencies: make sure the module containing the referenced class is included in the current module’s dependency list, and if not, manually add the dependency.
2. Check the dependency versions: Make sure that the versions of the classes referenced in the module are compatible with the current module’s dependency versions. If the versions are not compatible, adjustments to the dependency versions or updating the project code to adapt to the new version may be necessary.
3. Check the compilation order of modules: if there are dependencies between multiple modules, make sure that the modules being depended on are compiled before the current module, this can be resolved by adjusting the compilation order of modules.
4. Cleaning up and recompiling: Sometimes compilation issues may arise due to cache problems during the compilation process. You can try clearing the project’s compilation cache and recompiling.
5. Check the visibility and access permissions of classes: If the referenced class has incorrect access permissions in other modules, it may result in compilation errors. Make sure that the visibility and access permissions of the class are set correctly.
6. Check the classpath and reference paths: make sure the paths of the referenced classes are properly set and correctly referenced in the code.

If the above methods do not solve the problem, you can try using debugging tools or checking the compile error logs to obtain more detailed error information. Then, further investigate and resolve the issue based on the error information.