result = result.substring(0,result.length()-1); is used just to remove the last trailing space.
package com.codegym.task.task18.task1803;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.lang.reflect.Array;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
/*
Most frequent bytes
*/
public class Solution {
public static void main(String[] args) throws Exception {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
FileInputStream file = new FileInputStream(reader.readLine());
HashMap<Character,Integer> dict = new HashMap<Character, Integer>();
while(file.available()>0){
int a = file.read();
char c = (char) a;
//System.out.println(c);
if(!dict.containsKey(c)){
dict.put(c,1);
}
else {
int t = dict.get(c);
dict.put(c,t+1);
}
}
file.close();
//System.out.println(dict);
Set<Character> max = new HashSet<Character>();
int maxi = 0;
for (Map.Entry<Character,Integer> entry: dict.entrySet()) {
if(entry.getValue() > maxi ){
maxi = entry.getValue();
//System.out.println(maxi+" "+entry.getValue());
}
}
for (Map.Entry<Character,Integer> entry: dict.entrySet()) {
if(entry.getValue() == maxi) {
max.add(entry.getKey());
//System.out.println(max);
}
}
String result = "";
for (char a : max) {
//System.out.print(a+" ");
result = result + a + " ";
}
result = result.substring(0,result.length()-1);
System.out.println(result);
}
}