public static void main(String[] args) {
        int len = 10;
        Random rand = new Random();
        int val;
        int max = 20;
        Map<Holder<Integer>, Integer> m = new HashMap<Holder<Integer>, Integer>(len);
        for (int i = 0; i < len; ++i) {
            val = rand.nextInt(max) + 1;
            m.put(new Holder<Integer>(Integer.valueOf(val)), val * val);
        }

        System.out.println(m);

        Holder<Integer> h;
        for (int i = 0; i < max; ++i) {
            h = new Holder<Integer>(Integer.valueOf(i + 1));
            System.out.println("" + i + ": " + m.containsKey(h) + "    " + m.get(h));
        }
    }