Please see why it's not passing ?

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Assistance appreciated. I create thread, I count occurrences and insert char with most occurrences into the map. Not passing...

Read file names from the console until the word "exit" is entered.
Pass the file name to the ReadThread thread.
The ReadThread thread should find the byte that occurs most frequently in the file, and add it to resultMap,
where the String parameter is the file name and the Integer parameter is the relevant byte.
Close the streams.

Requirements:

The program must read file names from the console until the word "exit" is entered.
For each file, create and start a ReadThread thread.
After each thread is start, ReadThread should create its own file input stream.
Then each thread must find the most frequently occurring byte in its file and add it to resultMap.
The file input stream in each thread must be closed.

package com.codegym.task.task18.task1823; import java.io.*; import java.util.HashMap; import java.util.Map; import java.util.TreeMap; /* Read file names from the console until the word "exit" is entered. Pass the file name to the ReadThread thread. The ReadThread thread should find the byte that occurs most frequently in the file, and add it to resultMap, where the String parameter is the file name and the Integer parameter is the relevant byte. Close the streams. Requirements: 1. The program must read file names from the console until the word "exit" is entered. 2. For each file, create and start a ReadThread thread. 3. After each thread is start, ReadThread should create its own file input stream. 4. Then each thread must find the most frequently occurring byte in its file and add it to resultMap. 5. The file input stream in each thread must be closed. */ public class Solution { public static Map<String, Integer> resultMap = new HashMap<String, Integer>(); public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String fName = ""; while(!fName.equals("exit")){ fName = reader.readLine(); ReadThread readThr = new ReadThread(fName); readThr.start(); } reader.close(); } public static class ReadThread extends Thread { private String fileName; public int i = Integer.MIN_VALUE; public Character c = 0; public ReadThread(String fileName) throws IOException { this.fileName = fileName; } public void run(){ try { FileInputStream fis = new FileInputStream(this.fileName); TreeMap<Character, Integer> map = new TreeMap<>(); //see if exists in map, then up the count, else insert to map with 1 as count while (fis.available() > 0){ map.merge((char) fis.read(), 1, Integer::sum); } fis.close(); //loop through treemap and find entry with highest int for (Map.Entry<Character, Integer> entry : map.entrySet()) { if (entry.getValue()> i){ c = entry.getKey(); } } //add the character that occurred the most to the HashMap, as an integer resultMap.put(this.fileName,Character.getNumericValue(c)); } catch (Exception e) { e.printStackTrace(); } } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

13 April 2020, 15:50

useful

#1 The first problem that I see is lines 27-31. The check for the word "exit" is after you pass the variable fname to the readThread constructor. This is throwing an exception where "exit" is being used to initiate the FileInputStream. Two patterns I use for logic like this are:

String fName = reader.readLine();
while(!fName.equals("exit")){
   ReadThread readThr = new ReadThread(fName);
   readThr.start();
   fName = reader.readLine();
}

while(true){
   String fName = reader.readLine();
   if(fName.equals("exit")) break;
   ReadThread readThr = new ReadThread(fName);
   readThr.start();
}

#2 The other problem is that accessing shared resources, such as the "resultMap" on 21, with threads has the chance of incorrect information being stored in the shared resource. This is because when one thread is accessing the resource the threading system could switch the CPU to another thread and overwrite the work being done by the prior thread. The results can be very unpredictable. You are going to need to lock the shared resource each time you access it to prevent this.

Johannes

Level 27 , Centurion, Pretoria, South-Africa

14 April 2020, 07:41

Thanks, I missed problem #1 in this task, I actually had the same problem in another task after this one, and modified it to be similar to yours above. The threads one makes sense, not used to threads, lol. I made the section where I access the map in my run() method synchronized, and now I'm further, but still not passing the requirement that says I should update the map with the most frequently occurring byte ?

Johannes

Level 27 , Centurion, Pretoria, South-Africa

14 April 2020, 07:41

public class Solution { public static Map<String, Integer> resultMap = new HashMap<String, Integer>(); public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String fName = ""; while(!fName.equals("exit")){ fName = reader.readLine(); if (!fName.equals("exit")){ ReadThread readThr = new ReadThread(fName); readThr.start(); } } reader.close(); } public static class ReadThread extends Thread { private String fileName; public int i = Integer.MIN_VALUE; public Character c = 0; public ReadThread(String fileName) throws IOException { this.fileName = fileName; } public void run(){ try { FileInputStream fis = new FileInputStream(this.fileName); TreeMap<Character, Integer> map = new TreeMap<>(); //see if exists in map, then up the count, else insert to map with 1 as count while (fis.available() > 0){ map.merge((char) fis.read(), 1, Integer::sum); } fis.close(); //loop through treemap and find entry with highest int for (Map.Entry<Character, Integer> entry : map.entrySet()) { if (entry.getValue()> i){ c = entry.getKey(); } } //add the character that occurred the most to the HashMap, as an integer synchronized (Solution.resultMap){ resultMap.put(this.fileName,Character.getNumericValue(c)); } } catch (Exception e) { e.printStackTrace(); } } } }

Guadalupe Gagnon

Level 37 , Tampa, United States

14 April 2020, 13:47

So the next issue, which i missed the first time, is now the logic that compare counts to determine which character has the greatest occurence:

for (Map.Entry<Character, Integer> entry : map.entrySet()) {
      if (entry.getValue()> i){
         c = entry.getKey();
   }
}

The variable 'i' is set to Integer.MIN_VALUE, which is good, the problem occurs in that i is never changed from that, such as the case that you are comparing character counts. This means that c will always be set to the last occurring character in the TreeSet, which is sorted by ASCII code and not by the occurrence value. You will want to fix that and, fingers crossed, the task should pass.

Johannes

Level 27 , Centurion, Pretoria, South-Africa

14 April 2020, 20:24

CANNOT believe that snippet of code made sense to me....Thank you so much!