jdk 9 compilation fails

[sreev]

[INFO] Compiling 25 source files to /Users/svaddi/SreeVaddi/source/github/sreev/bdg-formats/target/classes
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] Source option 1.5 is no longer supported. Use 1.6 or later.
[ERROR] Target option 1.5 is no longer supported. Use 1.6 or later.
[INFO] 2 errors
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4.232 s
[INFO] Finished at: 2018-05-19T07:42:19-07:00
[INFO] ------------------------------------------------------------------------

[heuermh]

Hello @sreev, thank you for submitting this issue!

Are you planning to use bdg-formats outside of Apache Spark? As far as I know, support for JDK 9/10 in Apache Spark is still some time off, and we won't bump downstream in ADAM until Spark does.

[fnothaft]

@heuermh agreed about not bumping to Java 9/10 until Spark does, but from looking at #166, it doesn't look like any of the changes would preclude us from still building against Java 8 (other than the explicit bump to Java 9, of course, but we could take all of the change except for that). If that's the case, then I'd suggest we merge so that the eventual move to Java 9/10 is easier.