I dont understand what is wrong

Question about the task

Most frequent bytes

Java Core, Level 8, Lesson 3

Resolved

It even doesn't print anything

package com.codegym.task.task18.task1803; import java.io.FileInputStream; import java.io.*; import java.util.ArrayList; import java.util.HashMap; import java.util.Iterator; import java.util.Map; /* Most frequent bytes */ public class Solution { public static void main(String[] args) throws Exception { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); FileInputStream fileInputStream = new FileInputStream(reader.readLine()); ArrayList<Integer> list = new ArrayList<>(); HashMap<Integer, Integer > map = new HashMap<Integer, Integer>(); Iterator<Map.Entry<Integer, Integer>> iterator = map.entrySet().iterator(); while(fileInputStream.available() > 0){ int data = fileInputStream.read(); list.add(data); } int count ; int max; // boolean pass ; for (int j = 0 ; j< list.size(); j++){ count = 0; boolean pass = true; for (int i = 0; i< list.size() ; i++){ while(iterator.hasNext()){ Map.Entry<Integer, Integer> pair = iterator.next(); Integer key = pair.getKey(); if(list.get(j).equals(key)){ pass = false; } } if (list.get(j).equals(list.get(i))) count++; } if (pass == true) map.put(list.get(j), count); } Integer maxKey = 0; Integer maxValue = Integer.MIN_VALUE; while(iterator.hasNext()){ Map.Entry<Integer, Integer> pair = iterator.next(); Integer Key = pair.getKey(); Integer Value = pair.getValue(); if (Value > maxValue) { maxValue = Value; maxKey = Key; } } for (int i = 0 ; i< maxValue ; i++){ System.out.print( maxKey+ " "); } reader.close(); fileInputStream.close(); } }

Comments (3)

Popular
New
Old

You must be signed in to leave a comment

Guadalupe Gagnon

Level 37 , Tampa, United States

11 June 2020, 15:06

solution

Iterator objects are one way streets. They can only access the values that are currently inside the Collection that is used to create the Iterator. The only legal modifications need to use the Iterator's methods. Since the Iterator in this code is created on line 23 when the Collection "map" has no containing values, lines 37 and 52 are never reached because hasNext() will always be false. The while the loop at line 32, used to fill the map with the data counts, actually fills the map up correctly, however the inner loop at lines 36-42 is never used. You can see that by adding some sys.out statements:

for (int j = 0 ; j< list.size(); j++){
   count  = 0;
   boolean pass = true;
   for (int i = 0; i< list.size() ; i++){
      while(iterator.hasNext()){
         //↓add this line. It wont display because its never reached
         System.out.println("This line reached meaning hasNext() was true");
         Map.Entry<Integer, Integer> pair = iterator.next();
         Integer key = pair.getKey();
         if(list.get(j).equals(key)){
            pass = false;
         }
      }
      if (list.get(j).equals(list.get(i)))
         count++;
   }
   if (pass == true)
      map.put(list.get(j), count);
}
// ↓add this line which shows the counts contained in map
System.out.println(map);

By removing the unnecessary code, the code would work the exact same like this:

for (int j = 0 ; j< list.size(); j++) {
   count = 0;

   for (int i = 0; i < list.size(); i++) {
      if (list.get(j).equals(list.get(i)))
         count++;
   }

   map.put(list.get(j), count);
}

Up until line 51 the code looks fine. The code below this would work if the Iterator was used in the correct location. Also, at line 62, make sure you print out all the bytes that have the same maxValue, as there may be multiple keys with the same count.

Guadalupe Gagnon

Level 37 , Tampa, United States

11 June 2020, 16:30

useful

But the Iterator is a separate object from the Map. It is only filled with the items from the map when it is first declared, not with subsequent items. If you add items to a map, then create an iterator, then add more items to a map; when the iterator.next() method is called then a ConcurrentModificationException will be thrown. In the code above you create the iterator before adding any items to the map. This means that iterator.hasNext() will always return false and the lines of code that call iterator.next() can not be reached. No exception would occur.

David

Level 26 , Bucharest, Romania

11 June 2020, 19:41

I got it!! Thank you very much! It passed the test but doesn't print anything