question: private static byte [ ] ip4ToIp6 ( byte [ ] ip4 ) { if ( ip4 . length != 4 ) throw new IllegalArgumentException ( "IPv4 address must be four octets" ) ; byte [ ] ip6 = new byte [ 16 ] ; for ( int i = 0 ; i < 16 - 4 ; i ++ ) ip6 [ i ] = 0 ; for ( int i = 0 ; i < 4 ; i ++ ) ip6 [ 12 + i ] = ip4 [ i ] ; return ip6 ; }
target:  Convert an IPv4 address to an IPv6 IPv4-compatible address.