Why does it not work?

Question about the task

Symbol frequency

Java Core, Level 8, Lesson 11

Resolved

I have tested with several ASCII symbols and it works great

The program is started with one argument: the name of a file that contains text.
Calculate how often each symbol is encountered.
Sort the results by increasing ASCII code (read about it online).

Example:
','=44, 's'=115, 't'=116.

Display the sorted results:
[symbol1] frequency1
[symbol2] frequency2
Close the streams.

Example output:
, 19 - 7 f 361

Requirements:

You don't need to read anything from the console.
Create a stream to read from the file passed as the first argument of the main method.
You need to calculate the frequency of each symbol in the file and display the results.
The displayed results should be sorted by ascending ASCII code.
The stream used to read the file must be closed.

package com.codegym.task.task18.task1821; /* Symbol frequency */ import java.io.*; import java.util.ArrayList; import java.util.Map; import java.util.TreeMap; public class Solution { public static void main(String[] args) throws IOException { FileReader fileReader = new FileReader(args[0]); TreeMap<Character, Integer> map = new TreeMap<>(); ArrayList<Character> charList = new ArrayList<>(); ArrayList<Integer> ASCIIlist = new ArrayList<>(); int counter = 0; while (fileReader.ready()) { int data = fileReader.read(); ASCIIlist.add(data); } fileReader.close(); for (int i = 0; i < ASCIIlist.size(); i++) { charList.add((char)Integer.parseInt(String.valueOf(ASCIIlist.get(i)))); } // convers bytes into chars for (int i = 0; i<charList.size(); i++) { if (map.containsKey(charList.get(i))) { counter++; map.replace(charList.get(i), counter); } // if map contains char counter will go up, update map else { map.put(charList.get(i), counter); counter = 1; } // if map does not contain char, add it into map, set counter and restart counter } for (Map.Entry<Character,Integer> copy : map.entrySet()) { System.out.println(copy.getKey()+ " "+copy.getValue()); } } }

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Thomas

Level 41 , Bayreuth, Germany

15 May 2020, 12:23

solution

The conter thingie won't work as you wish. Imagine the first char in the list to be a 't', it's already in your map. Then you increment the counter and update the map. But what is the initial value of the counter? If the char before was eg. a 's' and that wasn't in the map, then the counter is set to 1. The counter variable has nothing to do with your map. So loop through your list and check for each char if it's already in the map. If not: put (current char, 1) if yes, replace(currentChar, (get(currentChar) + 1) Lines 28-30 are redundant, too as you can directly add the read data to your char list charList.add((char) fileReader.read()); And even that you do not need to do. Read the char and directly update your map (no need for a single list).

Rafał Pawłowski

Level 22 , Southampton, United Kingdom

15 May 2020, 12:34

It worked but I do not understand why it worked.

for (int i = 0; i<charList.size(); i++) {
            if (map.containsKey(charList.get(i))) {
                map.replace(charList.get(i), map.get(charList.get(i))+1);
            }
            else {
                map.put(charList.get(i), 1);
            }

I do not understand this part:

if (map.containsKey(charList.get(i))) {
                map.replace(charList.get(i), map.get(charList.get(i))+1);
            }

Let's assume I am looking for character 'c'. If map's key is 'c' then replace key with 'c' (I understand) and replace value with 'c'+1 (I do not understand). If it is ASCII c+1 will mean different character than c.

Thomas

Level 41 , Bayreuth, Germany

15 May 2020, 13:01

You replace it with the the value you get from your map for the key (in your example) 'c' and that value you increment by 1.