Some users have reported that Java may crash when starting DbVisualizer or when right-click to show menus. To workaround this open Tools->Tool Properties and select the General / Appearance category. Switch to a non Synthetica look and feel, click OK and restart.
Update 2017-12-11: From DbVisualizer 10.0.5 there is a fix for Synthetica that has been confirmed successful for users having this problem.