sorted

.java

HashMap<String, Integer> origens = new HashMap<>();
        for(Flight f: listOfFlights) {
            if(!origens.containsKey(f.getOrigin())) {
                origens.put(f.getOrigin(), 1);
            } else {
                Integer currentCount = origens.get(f.getOrigin());
                origens.replace(f.getOrigin(), currentCount + 1);
            }
        }

        Comparator<String> comparator = new ValueComparator(origens);
        //TreeMap is a map sorted by its keys.
        //The comparator is used to sort the TreeMap by keys.
        TreeMap<String, Integer> result = new TreeMap<String, Integer>(comparator);
        result.putAll(origens);

         System.out.printf(String.format("%-20s %-2s" , "Origem", "Voos\n"));

        for(Map.Entry<String, Integer> f: result.entrySet()) {
            System.out.printf(String.format("%-20s %-2s" , f.getKey(), f.getValue() + "\n"));
        }


 static class ValueComparator implements Comparator<String>{

        HashMap<String, Integer> map = new HashMap<String, Integer>();

        public ValueComparator(HashMap<String, Integer> map){
            this.map.putAll(map);
        }

        @Override
        public int compare(String s1, String s2) {
            if(map.get(s1) >= map.get(s2)){
                return -1;
            }else{
                return 1;
            }
        }
    }