public static Ip4Address makeMaskPrefix(int prefixLength) {
        byte[] mask = IpAddress.makeMaskPrefixArray(VERSION, prefixLength);
        return new Ip4Address(mask);
    }
@Test
    public void testMakeMaskPrefixIPv4() {
        Ip4Address ipAddress;

        ipAddress = Ip4Address.makeMaskPrefix(25);
        assertThat(ipAddress.toString(), is("255.255.255.128"));

        ipAddress = Ip4Address.makeMaskPrefix(0);
        assertThat(ipAddress.toString(), is("0.0.0.0"));

        ipAddress = Ip4Address.makeMaskPrefix(32);
        assertThat(ipAddress.toString(), is("255.255.255.255"));
    }