CodeGym/Help with Java Tasks/I've been looking at this too long.

Level 29

Seattle

04.03.2019
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11comments

I've been looking at this too long.

Question about the task

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The meat of the program starts at line 51. When I test the output, it looks like it is doing the right thing. This one is twisting my brain. Any hits will be appreciated.

Read 2 file names from the console: file1 and file2.
Both files contain text, but file2 is an updated version of file1. Some of the lines are still the same.
You need to create a merged version of the lines by writing them to the lines list.
The ADDED and REMOVED labels can't be used consecutively—they must always separated by the SAME label.
The example includes empty lines for clarity.
Neither the original file nor the updated file have empty lines!

Example 1:
original updated merged file1: file2: Result: (lines) line1 line1 SAME line1 line2 REMOVED line2 line3 line3 SAME line3 line4 REMOVED line4 line5 line5 SAME line5 line0 ADDED line0 line1 line1 SAME line1 line2 REMOVED line2 line3 line3 SAME line3 line4 ADDED line4 line5 line5 SAME line5 line0 REMOVED line0

Example 2:
original updated merged file1: file2: Result: (lines) line1 line1 SAME line1 line0 ADDED line0

In the example, empty lines mean that the line is not in the specified file.

Requirements:

The Solution class must contain a LineItem class.
The Solution class must have an enum called Type.
The Solution class must have a public static List<LineItem> field called lines that is initialized immediately.
In the main(String[] args) method, the program must read file names from the console (use BufferedReader).
In the main(String[] args) method, the BufferedReader used for reading input from the console must be closed after use.
The program must read the contents of the first and second file (use FileReader).
The file input streams (FileReader) must be closed.
The lines list should contain the merged version of the lines from the files. Each line should start with the label ADDED, REMOVED, or SAME, depending on the action taken.

package com.codegym.task.task19.task1916; import java.io.*; import java.util.ArrayList; import java.util.List; /* Tracking changes */ public class Solution { public static List<LineItem> lines = new ArrayList<>(); public static void main(String[] args) { //reads two file names from the console String file1 = null; String file2 = null; try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in))) { file1 = bufferedReader.readLine(); file2 = bufferedReader.readLine(); } catch (IOException e) { e.printStackTrace(); } //reads content from each file FileReader fileReader1 = null; FileReader fileReader2 = null; BufferedReader bufferedReader1 = null; BufferedReader bufferedReader2 = null; try { fileReader1 = new FileReader(file1); fileReader2 = new FileReader(file2); bufferedReader1 = new BufferedReader(fileReader1); bufferedReader2 = new BufferedReader(fileReader2); //reads all the contents of both files to lists List<String> linesFromOriginal = new ArrayList<>(); List<String> linesFromUpdated = new ArrayList<>(); while (bufferedReader1.ready()) { linesFromOriginal.add(bufferedReader1.readLine()); } while (bufferedReader2.ready()) { linesFromUpdated.add(bufferedReader2.readLine()); } //determines if each line from the file matches and adds entries to lines list int originalIndex = 0; int updatedIndex = 0; while ((updatedIndex < linesFromUpdated.size()) && (originalIndex < linesFromOriginal.size())) { String originalLine = linesFromOriginal.get(originalIndex); String updatedLine = linesFromUpdated.get(updatedIndex); if (updatedLine.equals(originalLine)) { lines.add(new LineItem(Type.SAME, updatedLine)); originalIndex++; updatedIndex++; } else if ((originalIndex + 1 < linesFromOriginal.size()) && (updatedLine.equals(linesFromOriginal.get(originalIndex + 1)))) { lines.add(new LineItem(Type.REMOVED, originalLine)); originalIndex++; } else { lines.add(new LineItem(Type.ADDED, updatedLine)); updatedIndex++; } } // //****************for testing // for (LineItem item : lines) { // System.out.println(item.type + ": " + item.line); // } // //****************end testing } catch (FileNotFoundException e) { System.out.println("File not found."); } catch (IOException e) { e.printStackTrace(); } finally { try { if (bufferedReader1 != null) bufferedReader1.close(); } catch (IOException e) { e.printStackTrace();} try { if (bufferedReader2 != null) bufferedReader2.close(); } catch (IOException e) { e.printStackTrace();} try { if (fileReader1 != null) fileReader1.close(); } catch (IOException e) { e.printStackTrace();} try { if (fileReader2 != null) fileReader2.close(); } catch (IOException e) { e.printStackTrace();} } } public static enum Type { ADDED, // New line added REMOVED, // Line deleted SAME // No change } public static class LineItem { public Type type; public String line; public LineItem(Type type, String line) { this.type = type; this.line = line; } } }

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Hashirama

Level 26 , Port-Harcourt, Nigeria

6 March 2019, 11:04

I followed your code but I missed it at lines 63 to 68. Could you explain these lines? Also, you don't need to close your streams when they are nulled. Just call the close() method on them after you're done.

Andrew

Level 29 , Seattle, United States

6 March 2019, 15:30

Sure, so starting from 59 (for context) this tests if the lines are the same. If they are not, on line 63 it tests the same line from the updated file with the next line in the original file. Because every other line has to be SAME, if the next line from the original file is equal to the updated line, then it means that the original file had an extra line that wasn't present in the updated file. Thus the updated file REMOVED the line. And finally, line 66, if the line isn't SAME or REMOVED it has to be ADDED. Let me know if you have anymore questions. Thanks for the tip about closing streams. I'm aware of that, yes. I'm using the if != null because I read here (https://javarevisited.blogspot.com/2014/10/right-way-to-close-inputstream-file-resource-in-java.html) about best practices for writing closing blocks and that is how they did it.

Guadalupe Gagnon

Level 37 , Tampa, United States

5 March 2019, 14:42

This one really twisted my brain when I first tried it. I finally did solve it, after many... MANY.. attempts. Have you read my question and subsequent hint? https://codegym.cc/help/1349

Andrew

Level 29 , Seattle, United States

5 March 2019, 15:31

Yes, I did read that and I think I've implemented what you said.

Andrew

Level 29 , Seattle, United States

5 March 2019, 16:12

Figured it out. I needed to add a bit to catch any extra items at the end of the files.

Andrew

Level 29 , Seattle, United States

5 March 2019, 16:15

Now it's taking issue with my closing of the FileReaders. I'm positive it's closing them, not sure what it wants.

Andrew

Level 29 , Seattle, United States

5 March 2019, 17:19

I changed it all to be simplified but it still says I need to close the FileReader:

String[] files = {file1, file2};
List<String> linesFromOriginal = new ArrayList<>();
List<String> linesFromUpdated = new ArrayList<>();

for (int i = 0; i < files.length; i++) {
    FileReader fileReader = new FileReader(files[i]);
    BufferedReader br = new BufferedReader(fileReader);

    while (br.ready()) {
        if (i == 0) {
            linesFromOriginal.add(br.readLine());
        } else {
            linesFromUpdated.add(br.readLine());
        }
    }

    br.close();
    fileReader.close();
}

Guadalupe Gagnon

Level 37 , Tampa, United States

5 March 2019, 20:42

I'll see about sharing my solve with you later. I need to find which computer it is on.

Andrew

Level 29 , Seattle, United States

5 March 2019, 21:34

Thanks.

Andrew

Level 29 , Seattle, United States

6 March 2019, 15:32

solution

I was able to get it to pass by using BufferedReader bufferedReader = new BufferedReader(new FileReader()), thanks Guadalupe! Devs, could you please take a look at this one because IMO it should pass however you use the FileReader. I also tried try with resources and it did not pass. Or was I doing it wrong somehow?

JianQiu Hwang

Level 35 , Washington

10 March 2020, 14:11

I hava get a right answer from first try, but I get wrong response with same reason with you. Just change to f**king

BufferedReader br1 = new BufferedReader(new FileReader(fileName1));

!!!