*(Since I got this error in a special situation where it actually makes sense to me.
I would like to share some insights and workarounds not mentioned elsewhere for similar questions here...)*

```
/* e.g. located in a src/main/java/mypkg/MyKeys.java file */
package mypkg;

public enum EditStatus { ... }
public enum CustomerTypeKey { ... }  // the suggestion of an IDE could be
                                     // to move this one to its own file
// ...

```

Now I want to have those types packed in one file as explained in my answer below...