After commenting in another discussion ( 18.2 crashes on start - win10 ) that I always download SQL Developer without the jdk I thought I would check which jdk the new 18.2 release ships with. Turns out it (the one in sqldeveloper\jdk\bin) is:
java version "9.0.4"
Java(TM) SE Runtime Environment (build 9.0.4+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.4+11, mixed mode)
but the download page claims it is JDK 8, so maybe the download page text (and the part about not supporting JDK 9 ! [Edit: In the release notes]) should be updated:

Message was edited by: Glen Conway