After you have your application working on JDK 16, here are some suggestions that can help you get the most from the Java SE Platform:
Cross-compile to an older release of the platform using the new
-–releaseflag in the javac tool, if required.
Take advantage of your IDE’s suggestions for updating your code with the latest features.
Find out if your code is using deprecated APIs by running the static analysis tool jdeprscan. As already mentioned in this guide, APIs can be removed from the JDK, but only with advance notice.
Get familiar with new features like multi-release JAR files (see jar).