public class Balls  {
    private static int compare(Integer o1, Integer o2) {
        if (o1 % 2 == 1) {
            return 1;
        }
        if (o1 % 2 != 1) {
            return -1;
        }
        return 0;
    }
    public static void main(String[] args) {
        Map<Integer, Integer> balls = new TreeMap<Integer, Integer>(Balls::compare);
for (int i = 0; i < 20; i++) {
            balls.put(i + 1, (int) (20 + Math.random() * 40));
        }
        System.out.println(balls.toString());
    }
}