We currently only support Java 6.
The current Java version is Java 8 and Java 9 is in development right now. We should aim to add support for Java 7 as soon as we can. This would also be useful for the OpenJDK port because IIRC it's problematic to get a JDK 6 on a Mac machine.
Java 7 support will become a hard requirement for us in JDK 10. In JDK 10, the source and target options for Java 6 will be removed from javac.
See https://bugs.openjdk.java.net/browse/JDK-8028563 for the bug for removal of Java 6 support in javac. The general source and target support policy can be found at http://openjdk.java.net/jeps/182 .