Android随机生成int数字永不重复

public class RandomId {
    private Random random;
    private String table;
    public RandomId() {
        random = new Random();
        table = "0123456789";
    }
    public String randomId() {
        int id=random.nextInt(10);
        String ret = null,
                num = String.format("%05d", id);
        int key = random.nextInt(10),
                seed = random.nextInt(100);
        Caesar caesar = new Caesar(table, seed);
        num = caesar.encode(key, num);
        ret = num
                + String.format("%01d", key)
                + String.format("%02d", seed);

        return ret;
    }

    public class Caesar {
        private String table;
        private int seedA = 1103515245;
        private int seedB = 12345;

        public Caesar(String table, int seed) {
            this.table = chaos(table, seed, table.length());
        }
        public Caesar(String table) {
            this(table, 11);
        }
        public Caesar() {
            this(11);
        }
        public Caesar(int seed) {
            this("ABCDEFGHIJKLMNOPQRSTUVWXYZ", seed);
        }
        public char dict(int i, boolean reverse) {
            int s = table.length(), index = reverse ? s - i : i;
            return table.charAt(index);
        }
        public int dict(char c,  boolean reverse) {
            int s = table.length(), index = table.indexOf(c);
            return reverse ? s - index : index;
        }
        public int seed(int seed) {
            long temp = seed;
            return (int)((temp * seedA + seedB) & 0x7fffffffL);
        }

        public String chaos(String data, int seed, int cnt) {
            StringBuffer buf = new StringBuffer(data);
            char tmp; int a, b, r = data.length();
            for (int i = 0; i < cnt; i += 1) {
                seed = seed(seed); a = seed % r;
                seed = seed(seed); b = seed % r;
                tmp = buf.charAt(a);
                buf.setCharAt(a, buf.charAt(b));
                buf.setCharAt(b, tmp);
            }
            return buf.toString();
        }

        public String crypto(boolean reverse,
                             int key, String text) {
            String ret = null;
            StringBuilder buf = new StringBuilder();
            int m, s = table.length(), e = text.length();

            for(int i = 0; i < e; i += 1) {
                m = dict(text.charAt(i), reverse);
                if (m < 0) break;
                m = m + key + i;
                buf.append(dict(m % s, reverse));
            }
            if (buf.length() == e)
                ret = buf.toString();
            return ret;
        }
        public String encode(int key, String text) {
            return crypto(false, key, text);

        }
        public String decode(int key, String text) {
            return crypto(true , key, text);
        }

//        public static void main(String[] args) {
//            Caesar caesar = new Caesar();
//            String data = caesar.encode(32, "APPLE");
//            caesar.decode(32, data);
//        }
    }

}