Подскажите, куда копать?
package com.javarush.task.task18.task1803;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/*
Самые частые байты
*/
public class Solution {
public static void main(String[] args) throws Exception {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String name = reader.readLine();
FileInputStream fileInputStream = new FileInputStream(name);
Map <Integer,Integer> map = new HashMap();
ArrayList list = new ArrayList();
while (fileInputStream.available()>0){
int data = fileInputStream.read();
list.add(data);
}
int maxrepit = 0;
int maxbite = 0;
for (int j = 0; j < 255; j++) {
int repeat = 0;
for (int i = 0; i<list.size(); i++){
if (list.get(i).equals(j))
repeat++;
}
map.put(repeat, j);
}
Integer maxKeys = 0;
List maxValue = new ArrayList<>();
for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
if (maxKeys == 0 || maxKeys.equals(entry.getKey())) {
maxKeys = entry.getKey();
maxValue.add(entry.getValue());
} else if (entry.getKey() > maxKeys) {
maxKeys = entry.getKey();
maxValue.clear();
maxValue.add(entry.getValue());
}
}
for (int i = 0; i < maxValue.size(); i++) {
System.out.print(maxValue.get(i)+" ");
}
fileInputStream.close();
}
}