java - duplicate class

this might be due to 2 classes with the same name in the same package

This can also happen if the package name does not match the folder name, or if the package name is omitted. Check the package statement in your source.

This is a known issue with netbeans BUG 226360

it might help to clear Netbeans cache:

Go to Help -> About and you will see

Cache directory: Path\to\Directory

Close NetBeans, go to specified directory and delete everything.