I found out Intellij supports drawing a class diagram or generating it from a given source package. See here for more details. The default for a field is to draw a 1-1 Composition connector (and 1-* Composition connector for arrays).
Is there any way to edit the multiplicity and to change the connector type (For example set the relationship to (1-3 aggregation)?
I couldn't find anything in the documentation, except a declaration that "IntelliJ IDEA follows the UML conventions"
It's not possible in IntelliJ IDEA at the moment, you can vote for the related feature request.