java.awt.Dialog.ModalityType has TOOLKIT_MODAL and APPLICATION_MODAL

The principal distinction between these was the case of multiple applets in the same VM in a browser.

Without that use case to all intents and purposes they are equivalent.
ie running a single application in a VM with the single toolkit that can be obtained, there's not much difference
There are some theoretical nuances
- Could you actually create a 2nd toolkit ?
- Could you run two applications ?

But there's not enough support in the JDK to do that

We should figure out what to say in the docs.
Note that the java.awt package doc also lists to an "AWT Modality" specification that also touches on this.