Mode of characters in string (highest frequency char in stri

  import java.io.*;
  import java.util.*;

  class MyCode {

   /**
    * 6 Character Mode
    *
    * Given a string, find the most frequent occurring letter(s) in the string
    *
    * Parameters
    * Input: string {String}
    * Output: {String}
    *
    * Constraints
    * If more than one letter is tied for the most frequent, return a string of all
    * the letters in one string.
    *
    * Time: O(N)
    * Space: O(N)
    *
    * Examples
    * 'hello' --> 'l'
    * 'A walk in the park' --> 'a'
    * 'noon' --> 'no'
    */
    public static void main (String[] args) {
      String one = "hello" ;
      String three = "A walk in the park";
      String four = "Awalkinthepark";

      String two = "noon";
      System.out.println(characterMode(two));
    }
     public static String characterMode(String string) {
       int count = 0;
       string = string.replaceAll("\\s", "");
       string = string.toLowerCase();
       HashMap<Character, Integer> map = new HashMap<Character,Integer>();
       //put chars from string into HashMap for tally
       for(int i = 0; i< string.length(); i++){
         if(map.containsKey(string.charAt(i))){
           count = map.get(string.charAt(i));
           map.put(string.charAt(i), ++count);
         }else{
            map.put(string.charAt(i), 1);
         }
       }
       //get highest value/count in map and append matching key to string
       int max = Collections.max(map.values());
       StringBuilder resultString = new StringBuilder("");
       for (Character c: map.keySet()) {
          if (map.get(c).equals(max)) {
            resultString.append(c);
          }
      }
       return resultString.toString();
     }
  }