I'm missing the "Then each thread must find the most frequently occurring byte in its file and add it to resultMap." part.

Question about the task

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Hi there, I'm to lazy to test this on test data. Can some1 glance over this and tell give me a hint. It's almost Christmas after all =P. Sorry for the missing comments in the code, i didn't think i'd have to ask for help on this one.

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; /* Threads and bytes */ public class Solution { public static Map<String, Integer> resultMap = new HashMap<String, Integer>(); public static void main(String[] args) throws Exception{ BufferedReader bf = new BufferedReader(new InputStreamReader(System.in)); String s = ""; while (true){ s = bf.readLine(); if("exit".equals(s)){ break; } ReadThread rt = new ReadThread(s); rt.start(); } bf.close(); } public static class ReadThread extends Thread { private String fn; public ReadThread(String fileName) { // Implement constructor body this.fn = fileName; } // Implement file reading here public void run() { try { FileInputStream fis = new FileInputStream(fn); HashMap<Integer, Integer> temp = new HashMap(); while (fis.available() > 0) { int a = fis.read(); int max = 1; if (temp.containsKey(a)) { temp.put(a, (temp.get(a) + 1)); if (temp.get(a) > max) { max = temp.get(a); } } else { temp.putIfAbsent(a, 1); } fis.close(); for (Map.Entry<Integer, Integer> entry : temp.entrySet()) { if (entry.getValue() == max) { synchronized (resultMap){ resultMap.put(fn, entry.getKey());} } } } } catch (Exception e) { } } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

14 December 2020, 15:06

solution

The mistake is very simple. Consider line 62. Not wanting to test your work is not going to be an option if you become a programmer. If this task here was a real world assignment and you told your employer that this is what you created and have someone else test it I am sure they would be a little more than upset.

MoJo

Level 23 , Cairns, Australia

Expert

14 December 2020, 23:06

Well that's a rookie mistake. But still, i took the deceleration out of the while loop and still don't get validation... Can't post my code because of the limit, but it's the same as before with the "int max = 1" just before the "while(fis.available > 0)"...

MoJo

Level 23 , Cairns, Australia

Expert

14 December 2020, 23:15

+ the testing checked out for real this time. Is it maybe because my is putting the same key with different bytes when several bytes occur "max" amount. But i tested

/*... line 78 ->*/
 for (Map.Entry<Integer, Integer> entry : temp.entrySet()) {
                        if (entry.getValue() == max) {
                            synchronized (resultMap){
                            resultMap.put(fn, entry.getKey());
break;   // <--------

                        }
                    }

so after the first "put" it would stop, but it is still not valid.

Guadalupe Gagnon

Level 37 , Tampa, United States

15 December 2020, 14:28

I would have assumed that if there were multiple bytes that were all the "most" that they all had to be added to the map too. However, with maps, the keys have to be unique while the value do not have to be. This means in this task that only one "max byte" can be added to the map per file name. Maybe the validation system checks that only 1 entry is made per filename? Also, I should have noticed this at first too, but line 75 is in the wrong place. I think you probably have already caught that.

MoJo

Level 23 , Cairns, Australia

Expert

15 December 2020, 19:43

That's what i mean, it's only possible to have one entry per filename (key). And that's why i tried the added "break;" in line 6 of my previous comment so it stops after the first occurrence of the most frequent(s) byte(s). But this did not help. Is line 75 in the wrong place? Closing the streams is supposed to save resources right? So my thought was/is to free those resources asap, in line 75. Or is there more to this?

MoJo

Level 23 , Cairns, Australia

Expert

15 December 2020, 19:52

LOL, now i see what's wrong This task makes me look bad. I closed the while loop way too late... Now i wonder why my testing worked at all... This is what it's supposed to look like:

while (fis.available() > 0) {
                    int a = fis.read();


                    if (temp.containsKey(a)) {
                        temp.put(a, (temp.get(a) + 1));

                        if (temp.get(a) > max) {
                            max = temp.get(a);
                        }

                    } else {
                        temp.putIfAbsent(a, 1);
                    }
                }

                fis.close();



                for (Map.Entry<Integer, Integer> entry : temp.entrySet()) {

                    if (entry.getValue() == max) {

                        synchronized (resultMap){
                            resultMap.put(fn, entry.getKey());}

                    } }

Guadalupe Gagnon

Level 37 , Tampa, United States

15 December 2020, 21:18