統計字串字元個數

import java.security.Key;
import java.util.Scanner;
import java.util.Set;
import java.util.TreeMap;

public class Main {
    public static <scanner> void main(String[] args) {
        System.out.println("請輸入一個字串");
        Scanner sc = new Scanner(System.in);
        String S = sc.next();

        TreeMap<Character, Integer> tm = new TreeMap<Character, Integer>();
        for (int i = 0; i < S.length(); i++) {
            char c = S.charAt(i);
            Integer i1 = tm.get(c);
            if (i1 == null) {
                tm.put(c, 1);
            } else {
                i1++;
                tm.put(c, i1);
            }


        }

        StringBuilder stringBuilder = new StringBuilder();
        Set<Character> characters = tm.keySet();
        for (char c : characters) {
            int m = tm.get(c);
            stringBuilder.append(c).append("(").append(m).append(")");


        }
        String string = stringBuilder.toString();
        System.out.println(string);


    }
}