Note: This might just be that I'm super rusty at java and am missing something silly.

When I set my JAVA_HOME to a jdk9 path and mvn compile, I get:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-checkstyle-plugin:3.0.0:check (checkstyle) on 
project google-cloud-pom: Execution checkstyle of goal 
org.apache.maven.plugins:maven-checkstyle-plugin:3.0.0:check failed: Plugin 
org.apache.maven.plugins:maven-checkstyle-plugin:3.0.0 or one of its dependencies could 
not be resolved: Could not find artifact com.sun:tools:jar:1.7.0 at specified path
/Library/Java/JavaVirtualMachines/jdk-9.0.1.jdk/Contents/Home/../lib/tools.jar -> [Help 1]

When I set my JAVA_HOME to a jdk8 path and mvn compile, it works.

This seems to be a known issue with checkstyle. I'm not sure how org.apache.maven.plugins » maven-checkstyle-plugin (which we use) relates to github.com/checkstyle/checkstyle; their versioning seems quite different (github latest is 8.8, whereas maven latest is 3.0.0 ).

edit: the difference between the two seems to be that the github one is the checkstyle project itself, and the maven thing is just a maven plugin possibly using the checkstyle project?