Can I specify the order of the classes in class diagram?

Question

I can specify the participant order in Sequence diagram, like this:

participant A

participant B

Can I specify the order of classes like this:

line1 AClass,BClass

line2 CClass, DClass

If AClass and BClass are on the same line, then AClass comes before BClass.

This feature is very important, I don't want to add a class and cause the original diagram layout to get messy.