Java Data Type - 如何计算字符串中的特定字符

import java.util.HashMap;

public class Main {

  public static void main(String[] args) {
    HashMap<Character, Integer> map = new HashMap<Character, Integer>();
    String test = "BUNANA";
    char[] chars = test.toCharArray();

    for (int i = 0; i < chars.length; i++) {
      if (!map.containsKey(chars[i])) {
        map.put(chars[i], 1);
      }
      map.put(chars[i], map.get(chars[i]) + 1);
    }

    System.out.println(map.toString());
  }

}