Class UUID

CodenameOne/src/com/codename1/io/Util.java:3342–3455

    /// UUID u = new UUID().toString();
    /// ```
    static class UUID {

        /*
         * UUID - an implementation of the UUID specification for Codename One
         * by Francesco Galgani
         *
         * You can use this class as you want (public-domain license).
         */
        private static final char[] DIGITS = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
        private static final Random randomTime = new Random(System.currentTimeMillis());
        private static final Random randomClockSeqAndNode = new Random(getUniqueDeviceID());

        private long time = 0l;
        private long clockSeqAndNode = 0l;

        /// Constructor for UUID, it uses the system clock and some device info
        /// as seeds for random data, that are enough for practical usage.
        public UUID() {
            this.time = randomTime.nextLong();
            this.clockSeqAndNode = randomClockSeqAndNode.nextLong();
        }

        /// Constructs a UUID from two `long` values.
        ///
        /// #### Parameters
        ///
        /// - `time`: the upper 64 bits
        ///
        /// - `clockSeqAndNode`: the lower 64 bits
        public UUID(long time, long clockSeqAndNode) {
            this.time = time;
            this.clockSeqAndNode = clockSeqAndNode;
        }

        private static String append(String a, short in) {
            return append(a, (long) in, 4);
        }

        private static String append(String a, int in) {
            return append(a, (long) in, 8);
        }

        private static String append(String a, long in, int length) {
            int lim = (length << 2) - 4;
            StringBuilder sb = new StringBuilder(a);
            while (lim >= 0) {
                sb.append((DIGITS[(byte) (in >> lim) & 0x0f]));
                lim -= 4;
            }
            return sb.toString();
        }

        private static long getUniqueDeviceID() {
            long id = Preferences.get("CustomDeviceId__$", (long) -1);
            if (id == -1) {
                id = Preferences.get("DeviceId__$", (long) -1);
            }
            if (id == -1) {