/usr/lib/jvm/java-9-openjdk-amd64/demo/applets is in openjdk-9-demo 9~b114-0ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/jvm/java-9-openjdk-amd64/demo/../../../../share/doc/openjdk-9-jre-headless/demo/applets