CodeGym/Help with Java Tasks/The task failed to pass testing with these messages: "Do...

Level 23

Szekesfehervar

25.05.2021
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10comments

The task failed to pass testing with these messages: "Don't display the same byte several times." - "CodeGym security exception. You are performing a forbidden or potentially dangerous operation."

Question about the task

Resolved

What kind of forbidden or dangerous operation am I using??... And most importantly, what could be the basic bug in the program that is causing the test to fail? (The previous problem has been fixed: this program no longer contains static variables.)

package com.codegym.task.task18.task1803; import java.io.*; import java.util.*; /* Most frequent bytes */ public class Solution { public static void main(String[] args) throws Exception { Map<Integer, Integer> fileBytes = readFileToMap(); Integer highestValue = lookingForHighestValue(fileBytes); ArrayList<Integer> resultList = lookingForRepeatingValue(fileBytes, highestValue); printResults(resultList); } public static Map<Integer, Integer> readFileToMap() throws Exception { BufferedReader inputConsole = new BufferedReader(new InputStreamReader(System.in)); String fileName = inputConsole.readLine(); inputConsole.close(); BufferedInputStream inputFromFile = new BufferedInputStream(new FileInputStream("/uploads/file.txt")); Map<Integer, Integer> fileBytes = new HashMap<>(); while (inputFromFile.available()>0) { Integer byteRead = inputFromFile.read(); if (fileBytes.containsKey(byteRead)) { fileBytes.replace(byteRead, fileBytes.get(byteRead)+1); } else fileBytes.put(byteRead, 1); } inputFromFile.close(); return fileBytes; } public static Integer lookingForHighestValue(Map<Integer, Integer> fileBytes) { Integer highestValue=0; for (Integer val : fileBytes.values() ) { if (val.compareTo(highestValue) > 0) { highestValue = val; } } return highestValue; } public static ArrayList<Integer> lookingForRepeatingValue(Map<Integer, Integer> fileBytes, Integer highestValue) { ArrayList<Integer> resultList = new ArrayList<>(); for (Map.Entry<Integer, Integer> pair : fileBytes.entrySet() ) { if (pair.getValue().equals(highestValue)) { resultList.add(pair.getKey()); } } return resultList; } public static void printResults(ArrayList<Integer> resultList) { int count = 0; for( Integer textByte : resultList) { count++; System.out.print(textByte); if (count<resultList.size()) System.out.print(" "); } } }

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Guadalupe Gagnon

Level 37 , Tampa, United States

25 May 2021, 20:08

solution

you did change the file name from "/uploads/file.txt" to the filename read in from the keyboard? That is probably your security problem. Here is a technique I use for outputs:

public static void printResults(ArrayList<Integer> resultList) {
   Iterator<Integer> iter = resultList.iterator();
   System.out.print(iter.next()); // print first
   while (iter.hasNext()) System.out.print(" " + iter.next()); // print each other starting with a space
   System.out.println();
}

checking the count each time is extra work.

Gellert Varga

Level 23 , Szekesfehervar, Hungary

25 May 2021, 20:19

Oh, yes, I wrote it... on my favorite program-testing site I can only read files this way, and due to inattention I left this modification in:-/

Gellert Varga

Level 23 , Szekesfehervar, Hungary

25 May 2021, 20:24

printResults() : Nice solution:) But isn't iter.hasNext() that much extra work?

Guadalupe Gagnon

Level 37 , Tampa, United States

25 May 2021, 20:27

for( Integer textByte : resultList) {

That line uses an iterator.

Gellert Varga

Level 23 , Szekesfehervar, Hungary

25 May 2021, 20:28

It passed the test immediately after correcting the filename:)

Gellert Varga

Level 23 , Szekesfehervar, Hungary

25 May 2021, 20:30

Does this mean that this code also uses (in a built-in invisible way) hasNext?

Guadalupe Gagnon

Level 37 , Tampa, United States

25 May 2021, 20:34

useful

Yes. Classes have to implement the Iterable interface or they can not be used in a foreach loop.

Guadalupe Gagnon

Level 37 , Tampa, United States

25 May 2021, 20:37

useful

Example code:

public class Solution implements Iterable<String>{
    String[] temp = "just a simple test to demonstrate".split(" ");

    public static void main(String[] args) {
        Solution sol = new Solution();

        for(String x : sol){ // object of Solution class in foreach loop
            System.out.println(x);
        }
    }


    @Override
    public Iterator<String> iterator() {
        return Arrays.stream(temp).iterator();
    }
}

Try removing the implements Iterable and the code breaks.

Gellert Varga

Level 23 , Szekesfehervar, Hungary

25 May 2021, 20:56

What this means: Arrays.stream(temp) ?

Guadalupe Gagnon

Level 37 , Tampa, United States

25 May 2021, 23:57

its part of the stream api introduced in java 8. Codegym doesn't really talk about it, but i used it here so I didn't have to make my own iterator class... though I could do that too. Here is if I created my own Iterator.... Codegym talks about method classes and anonymous classes later on:

@Override
public Iterator<String> iterator() {
   return new Iterator<String> {
      int i = 0;

      @Override
      public String next() {
         return temp[i++];
      }

      @Override
      public boolean hasNext() {
         return i < temp.size();
      }
   };
}