[Java练习]输入一个字符串，输出其中某个小写字母出现的次数

package com.company;import java.sql.*;public class Main{    public static void main(String[] args) throws ClassNotFoundException, SQLException    {        System.out.println("请输入一个字符串：");        Scanner sc = new Scanner(System.in);        String str = sc.nextLine();        char[] ch = str.toCharArray();        char a1 = 'a';        while (a1<= 'z')        {            int n = 0;            for (int i = 0; i < ch.length; i++)            {                if (a1 == ch[i])                {                    n++;                }            }            if(n!=0) System.out.println(a1+": "+n+"个");            a1++;        }    }}