code: protected void leaveGroup(SocketAddress mcastaddr, NetworkInterface netIf)
          throws IOException {
          if (mcastaddr == null || !(mcastaddr instanceof InetSocketAddress))
              throw new IllegalArgumentException("Unsupported address type");
          leave(((InetSocketAddress)mcastaddr).getAddress(), netIf);
      }
docs: Leave the multicast group.
  @param mcastaddr multicast address to leave.
  @param netIf specified the local interface to leave the group at
  @throws  IllegalArgumentException if mcastaddr is null or is a
  SocketAddress subclass not supported by this socket
  @since 1.4