How to use classes in pipeline script?

[Lars Meynberg]

We want to group some information in an object rather then have multiple variables in the main pipeline script. 

I tried to create a class (First Java then Groovy) but every time when I try to init it in the script I got following error:

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:

WorkflowScript: 1: unable to resolve class classes.BuildEnvironment

 @ line 1, column 1.

   import classes.BuildEnvironment

The folder looks like this

simple_pipeline.groovy

external.groovy

classes/BuildEnvironment.groovy

The pipeline setup is attached.

Maybe someone can point out what I'm doing wrong.

[Lars Meynberg]

I'm aware that there is the possibility of the workflow-cps-global-lib-plugin but I like to now if it's possible without it or is that another groovy restriction for pipeline scripts like Closures?

[Sven Finsterwalder]

I have a similar problem with an enum class.
Has anyone a solution or a hint to solve that issue.