public class Test {

    public static void main(String[] args) {
        String[] strs = new String[]{"a","b","a"};
        Map<String, Integer> map = new HashMap<String, Integer>();
        for(String s : strs){
            Integer key = map.get(s);
            if(key == null){
                map.put(s, 1);
            }else{
                map.put(s, key.intValue() + 1);
            }
        }
        Set<Entry<String, Integer>> set = map.entrySet();
        List<Entry<String, Integer>> list = new ArrayList<Entry<String, Integer>>();
        Iterator<Entry<String, Integer>> iter = set.iterator();
        while(iter.hasNext()){
            list.add(iter.next());
        }
        Collections.sort(list, new ComparatorEntry());
        for(Entry<String, Integer> entry : list){
            System.out.println(entry.getKey() + " : " + entry.getValue());
        }
    }
}

class ComparatorEntry implements Comparator<Entry<String, Integer>>{
    @Override
    public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2) {
        return o2.getValue().intValue() - o1.getValue().intValue();
    }
}