PriorityQueue sort HashMap by value - character frequency

PriorityQueueSortMapValue.java

class Solution {
    public String frequencySort(String s) {
        if (s.length() < 1) return "";
        
        Map<Character, Integer> charMap = new HashMap<>();
        
        for (char ch : s.toCharArray()) {
            Integer count = charMap.get(ch);
            if (count != null) {
                charMap.put(ch, count + 1);
            } else {
                charMap.put(ch, 1);
            }
        }
        
        PriorityQueue<CharWithCount> pq = new PriorityQueue(charMap.size(), new Comparator<CharWithCount> () {
            @Override
            public int compare(CharWithCount c1, CharWithCount c2) {
                return c2.mCount - c1.mCount;
            }
        });
        
        for (char ch : charMap.keySet()) {
            int count = charMap.get(ch);
            pq.offer(new CharWithCount(ch, count));
        }
        
        StringBuilder sb = new StringBuilder();
        while (!pq.isEmpty()) {
            CharWithCount cwc = pq.poll();
            for (int i = 0; i < cwc.mCount; i++) {
                sb.append(cwc.mChar);
            }
        }
        
        return sb.toString();
        
    }
    
    class CharWithCount {
        public int mCount;
        public char mChar;
        public CharWithCount(char ch, int count) {
            mChar = ch;
            mCount = count;
        }
    }
}