I used it well before, I don’t know if I clicked the package path or where I clicked the toolbar location. Then almost every Java file in the project reported a Cannot resolve symbol error. Even if a statement like String reported an error, I can guarantee that all the referenced packages are referenced and there will be basically no conflicting classes.
Later hereBaidu knows, find this solution:
Click File | Invalidate Caches, clean the cache and restart IDEA.