I'm trying to make a modding api for my mods, but I don't know how to start. I've already made a few mods, but they have some really repetitive code. How do I make a mod with classes my other mods can use?

EDIT: Misunderstood.

It isn't as difficult as you think. It was pretty easy for me, even when I hardly knew java.

Eclipse has an export option, you need to export src/main/java, src/main/resources and the folder src.

In eclipse you have a toolbar above your files, you need project/properties/libraries/add external jar and than choose the jar you created with the export funtion.

I already did that, it worked fine whilst testing it in my modding environment.

However, as soon as I try to build it using Gradle, it fails because of "classes not found".

Are you sure you have exported all required folders?

You needed to export 3 folders.

Can you open the source folders from the mod that imports the other mod?