java中利用TreeMap实现统计键盘录入字符的出现次数

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

public class Zf_cishu {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        System.out.println("请输入一串字符:");
        String line=scanner.nextLine();
        char[] s=line.toCharArray();

        TreeMap<Character, Integer> treeMap=new TreeMap<>();
        for (char c : s) {
            if(treeMap.get(c)==null) {
                treeMap.put(c, 1);
            }else {
                int i=treeMap.get(c);
                i++;
                treeMap.put(c, i);
            }
        }
        StringBuilder stringBuilder=new StringBuilder();
        Set<Character> set=treeMap.keySet();
        for (Character c : set) {
            stringBuilder.append(c+"("+treeMap.get(c)+")");
        }
        System.out.println(stringBuilder);

    }

}