In Java SE 9 the requirement to support multicasting has been somewhat relaxed, in order to support a small number of platforms where multicasting is not available. The specification for the `java.net.MulticastSocket::joinGroup` and the `java.nio.channels.MulticastChannel::join` methods has been updated to indicate that an `UnsupportedOperationException` will be thrown if invoked on a platform that does not support multicasting.

There is no impact to Oracle JDK platforms, since they do support multicasting.