统计abcd出现的次数用数组或者HashMap

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

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
    public static void main (String[] args) throws java.lang.Exception
    {
        Scanner  sc = new Scanner(System.in);
        String s = sc.nextLine();
        char[] s1 = s.toLowerCase().toCharArray();
        int[] a = new int[4];
        for (int i = 0; i < s1.length; i++)
        {
            a[s1[i] - 'a']++;
        }
        for (int i = 0; i < 4; i++)
        {
            System.out.print(String.valueOf((char)('a' + i)) + a[i]  + " ");
        }
    }
}