Derby can't be built with JDK 9. Java 9 introduces new JDBC classes like java.sql.ShardingKey and methods which refer to these new classes.
In addition, project Jigsaw has created a new way to name classes (see http://openjdk.java.net/jeps/220). This breaks the PropertySetter build tool which we use so that old JVMs can compile Derby and so that Derby can be compiled to run on old JVMs.
It is likely that we will need to leave this issue open throughout the development cycle of Java 9.