Tested with JDeveloper Version 18.104.22.168, 22.214.171.124
Monitoring of the java heap size + the ability to force garbage collection.
Finally I found it as you can see from the screen shot above which shows my right bottom of JDeveloper Statusbar.
So how to activate this one? Well it is quite easy. Locate $MW_HOME/jdeveloper/jdev/bin/jdev.conf and add the following line at the bottom
That might save you from restarting Jdeveloper to often a day;)