It seems that setting jdk: openjdk8 on the .travis.yml file actually selects javac from Oracle JDK 9 (reproduced with Ubuntu 14.04.5 images).
I have created an issue for jdk_switcher with more details on the problem: https://github.com/michaelklishin/jdk_switcher/issues/20
As described in the issue, this actually seems to be bug in Ubuntu’s update-java-alternatives.
Possible workarounds could be:
- Patch update-java-alternatives (a patch is already available in the Debian / Ubuntu bug reports linked in the Github issue above)
- Patch the .jinfo file from openjdk-8 and either replace the “jdkhl” tags with “jdk” or duplicate all “jdkhl” entries with new entries tagged “jdk”