JGraphT create a random graph from pre existing vertices

I need to create a random graph from a few pre existing vertices. I didn't find a way to do this yet. Each tutorial is using the "VertexFactory" (which btw cannot be resolved even though importing org.jgraph.generate.*) to make up vertices while creating the graph. But I rather would like to generate the graph from already existing vertices. I'm especially interested in the WattsStragotz algorithm but I don't know yet. Is this possible with using the already written RandomGeneration classes of Jgrapht?

Thanks a lot