public static void main(String[] args) {
    class Entry { 
        public int number; 
        public int count = 1;
    };
    Entry[] arr = new Entry[20];
    java.util.Random rand = new java.util.Random();
    int min = 0;
    int max = 0;
    int maxVal = 0;
    for (int i = 0, num, count = 0; count < arr.length && i < arr.length; count++) {
        num = rand.nextInt(10);
        if (min > num) min = num;
        if (max < num) max = num;
        boolean notFound = true;
        for (int j = 0; j < arr.length && arr[j] != null; j++) { // не оптимальное решение !
            if (arr[j].number == num) {
                arr[j].count++;
                notFound = false;
                if (maxVal < arr[j].count) maxVal = arr[j].count; 
                break;
            }
        }
        if (notFound) {
            arr[i] = new Entry();
            arr[i++].number = num;
        }
    }
    
    System.out.print("До сортировки: ");
    for (Entry e: arr) {
        if (e == null) break;
        System.out.print(e.number + "=" + e.count + "; ");
    }
    System.out.println();
    
    Arrays.sort(arr, new Comparator<Entry>() {
        @Override
        public int compare(Entry o1, Entry o2) {
            return o1 != null && o2 != null ? o1.number - o2.number : 0;
        }
    });
    
    System.out.print("После сортировки: ");
    for (Entry e: arr) {
        if (e == null) break;
        System.out.print(e.number + "=" + e.count + "; ");
    }
    System.out.println();

    System.out.println(min + " - минимальное число");
    System.out.println(max + " - максимальное число");
    System.out.println(maxVal + " - максимальное число повторений"); 
}