public static Ip6Address makeMaskPrefix(int prefixLength) {
        byte[] mask = IpAddress.makeMaskPrefixArray(VERSION, prefixLength);
        return new Ip6Address(mask);
    }
@Test
    public void testMakeMaskPrefixIPv6() {
        Ip6Address ipAddress;

        ipAddress = Ip6Address.makeMaskPrefix(8);
        assertThat(ipAddress.toString(), is("ff00::"));

        ipAddress = Ip6Address.makeMaskPrefix(120);
        assertThat(ipAddress.toString(),
                   is("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ff00"));

        ipAddress = Ip6Address.makeMaskPrefix(0);
        assertThat(ipAddress.toString(), is("::"));

        ipAddress = Ip6Address.makeMaskPrefix(128);
        assertThat(ipAddress.toString(),
                   is("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff"));

        ipAddress = Ip6Address.makeMaskPrefix(64);
        assertThat(ipAddress.toString(), is("ffff:ffff:ffff:ffff::"));
    }