If I understand you correctly, you want to manipulate/use a list of mendix objects in a java action?
If that is the case, I'd suggest setting the input parameter of the java action to "list" and sending it as a parameter in that way. (As Robert noted)
The wacky alternative is to create a Domain Entity that has a referenceset to the list of objects that you want to pass, then add that entity to the java action as a parameter, and retrieve the list inside the java action.
If you explicitly want to send a list via a "any object" parameter, please file a feature request in MXDN.
You can select 'List' as one of the parameters for the java action.
Edit: Ah seems I misunderstood. You can't pass a list of variables without connecting them to objects no.