Here we go again… find the correct shell script or configuration file and change one line there… This time it’s $JDEVELOPER_PRODUCT_HOME/<version>/product.conf. There just find SetJavaHome directive (it will be one of the first) and alter per your wish:
#
# By default, the product launcher will search for a JDK to use, and if none
# can be found, it will ask for the location of a JDK and store its location
# in this file. If a particular JDK should be used instead, uncomment the
# line below and set the path to your preferred JDK.
#
SetJavaHome /opt/jvm/jdk1.8.0_251
BTW, if you are curious, where is the $JDEVELOPER_PRODUCT_HOME located, it’s always $HOME/.jdeveloper and you can’t change it (as far as I know). I was able to get rid off system directory and move elsewhere, but this product.conf is still here… but I don’t care as it is not that much.