не понятно, что не так.
package com.javarush.task.task18.task1803;
/*
Самые частые байты
*/
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
public class Solution {
public static void main(String[] args) throws Exception {
int count;
Map<Integer, Integer> map=new HashMap<>();
ArrayList<Integer> list = new ArrayList<>();
ArrayList<Integer> num = new ArrayList<>();
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
FileInputStream fileName = new FileInputStream(reader.readLine());
while (fileName.available() > 0) {
list.add(fileName.read());
}
fileName.close();
for (Integer elem : list) {
count = Collections.frequency(list, elem);
map.put(elem, count);
num.add(count);
}
int max=Collections.max(num);
System.out.print(map.get(max)+" ");
}
}