CodeGym/Help with Java Tasks/Why won't it verify? The output is as requested

Level 41

08.02.2021
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Why won't it verify? The output is as requested

Question about the task

Resolved

Is it because in case the files have more lines than 6 it won't work?

if (counterFile1 == 6){
                while (true) {
                    if (LinesFile1.get(counterFile1).equals(LinesFile2.get(counterFile2))) {
                        lines.add(new LineItem(Type.SAME, LinesFile2.get(counterFile2)));
                        counterFile2++;
                    } else {
                        lines.add(new LineItem(Type.ADDED, LinesFile2.get(counterFile2)));
                        counterFile2++;
                        if (counterFile1 == LinesFile1.size()) break;
                    }
                    if ( counterFile2 == LinesFile2.size()) break;
                }
            }

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.BufferedReader; import java.io.FileReader; import java.io.InputStreamReader; 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) throws Exception { BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in)); String file1 = bufferedReader.readLine(); String file2 = bufferedReader.readLine(); bufferedReader.close(); BufferedReader bufferedReader1 = new BufferedReader(new FileReader(file1)); BufferedReader bufferedReader2 = new BufferedReader(new FileReader(file2)); /* I was over thinking it and the key was the restriction that "The ADDED and REMOVED labels can't be used consecutively". This means that when you either ADDED or REMOVED a line (and there are still lines to be parsed), then the next one has to be SAME. Basically you have to test each line of the file and if they are the same: lines.add(new LineItem(Type.SAME, theFullLine)); and move your counter for each by 1 if they are different check to see if the next line from the original matches, if true: lines.add(new LineItem(Type.REMOVED, theFullLine)); and move only the counter from file 1 and if false lines.add(new LineItem(Type.ADDED, theFullLine)); and move only the counter from the second file */ List<String> LinesFile1 = new ArrayList<>(); List<String> LinesFile2 = new ArrayList<>(); while (true){ LinesFile1.add(bufferedReader1.readLine()); LinesFile2.add(bufferedReader2.readLine()); if ((!(bufferedReader1.ready()) && (!bufferedReader2.ready()))) break; } bufferedReader1.close(); bufferedReader2.close(); int counterFile1 = 0; int counterFile2 = 0; String lineFile1; String lineFile2; for (int i = 0; i < LinesFile2.size(); i++){ //6,6,5 lineFile1 = LinesFile1.get(counterFile1); lineFile2 = LinesFile2.get(counterFile2); if (lineFile1.equals(lineFile2)) { lines.add(new LineItem(Type.SAME, lineFile1)); counterFile1++; counterFile2++; } else { lineFile1 = LinesFile1.get(counterFile1+1); if (lineFile1.equals(lineFile2)) { lines.add(new LineItem(Type.REMOVED, LinesFile1.get(i))); counterFile1++; } else { lines.add(new LineItem(Type.ADDED, lineFile2)); counterFile2++; } } if (counterFile1 == 6){ while (true) { if (LinesFile1.get(counterFile1).equals(LinesFile2.get(counterFile2))) { lines.add(new LineItem(Type.SAME, LinesFile2.get(counterFile2))); counterFile2++; } else { lines.add(new LineItem(Type.ADDED, LinesFile2.get(counterFile2))); counterFile2++; if (counterFile1 == LinesFile1.size()) break; } if ( counterFile2 == LinesFile2.size()) break; } } } //main bracket for (LineItem line : lines) System.out.println(line.toString()); System.out.println(counterFile1); System.out.println(counterFile2); } 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 String toString() { return String.format("LineItem{%s - %s}", type, line); } public LineItem(Type type, String line) { this.type = type; this.line = line; } } }

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Mike McKenna

Level 25 , Wilmington, United States

8 February 2021, 23:01

Hi Andrei, Guadalupe is very helpful . I am going to add his comments to my saved information .

Guadalupe Gagnon

Level 37 , Tampa, United States

8 February 2021, 15:46

useful

In this task there are only 3 possibilities of any two set of lines, either you will add: SAME SAME line 1 - line 1 line 2 - line 2 REMOVE SAME line 1 - line 2 - line 2 or ADDED SAME - line 1 line 2 - line 2 (or you reach the end of the file) The first problem that I see with your code is that the loop you use on line 16 only loops as long as i is less than file2 size. This is going to be a problem if file1 is very large while file 2 is very short, meaning there are a lot of lines that are removed. So if the files had lines like this: line 1 - line 2 line 2 - line 4 line 3 - line 6 line 4 line 5 line 6 This would be valid where the correct results would be: REM line 1 SAM line 2 REM line 3 SAM line 4 REM line 5 SAM line 6 And that if statement: if (counterFile1 == 6){ would mean this code would only work if File1 had exactly 6 lines, up to that point. The input files could be any size from a couple lines to thousands. Even in my example, the code in that statement wouldn't be reached because the for loop would break after 3 cycles, because that is how many lines file2 would have

Andrei

Level 41

8 February 2021, 15:59

Oh man, I thought the files were of the same size but I guess I should be thinking of a 'worldwide' applicability for this exercise. Man, this is difficult. Do you have any pointers as to how I could approach this?

Guadalupe Gagnon

Level 37 , Tampa, United States

8 February 2021, 16:26

I think your code is actually fairly close to a correct solution, just need to make a few changes: - Make sure the loop reading the lines from the file doesn't end up putting a bunch of 'null' values in one of the lists - change the loop at line 63 to continue as long as there are more lines in either file - take into account that one file may reach the end before the other file. Line 73 would be problematic if the first file reached the end before the second file (this line would result in an IndexOutOfBoundsException)

Andrei

Level 41

9 February 2021, 07:32

But how can the reader put null values in a list if it has finished reading? I mean, a reader, can it just read infinitely even after there are no more bytes to read? I have changed the loop and made it 2 loops.

while (bufferedReader1.ready()){
            LinesFile1.add(bufferedReader1.readLine());
        }
        while (bufferedReader2.ready()) {
            LinesFile2.add(bufferedReader2.readLine());
        }

Andrei

Level 41

9 February 2021, 08:01

I believe I have tackled this issue "- take into account that one file may reach the end before the other file. Line 73 would be problematic if the first file reached the end before the second file (this line would result in an IndexOutOfBoundsException)" by reformatting the block like this:

//continue loop as long as there are more lines in either file
       for (int i = 0; i < LinesFile2.size() || i < LinesFile1.size(); i++){ //6,6,5
           lineFile1 = LinesFile1.get(counterFile1);
           lineFile2 = LinesFile2.get(counterFile2);
           if (lineFile1.equals(lineFile2))
           {
               lines.add(new LineItem(Type.SAME, lineFile1));
               if (counterFile1 == LinesFile1.size()-1) counterFile1 = LinesFile1.size()-1;
               else counterFile1++;
               counterFile2++;
           }
           else {
               //one file may reach the end before the other file
               if (counterFile1 == LinesFile1.size()-1) lineFile1 = LinesFile1.get(counterFile1-1);
               else lineFile1 = LinesFile1.get(counterFile1+1);
               if (lineFile1.equals(lineFile2)) {
                   lines.add(new LineItem(Type.REMOVED, LinesFile1.get(i)));
                   counterFile1++;
               }
               else {
                   lines.add(new LineItem(Type.ADDED, lineFile2));
                   counterFile2++;
               }

I added those 2 if else blocks

Andrei

Level 41

9 February 2021, 08:04

But with these it still not solves the issue of not adding the last 2 lines from file 2. LineItem{SAME - line one is going to be the same} LineItem{REMOVED - line two is going to be removed} LineItem{SAME - line three is going to be the same} LineItem{REMOVED - line four is going to be removed} LineItem{SAME - line five is going to be the same} LineItem{ADDED - line six is going to be added} LineItem{SAME - line seven is going to be the same} It's missing these 2 : LineItem{ADDED - line eight is going to be added} LineItem{SAME - line nine is going to be the same}]

Nouser

Level 36 , Germany

9 February 2021, 09:20

You're running into problems when reaching the end of the files. There are several approaches to address this. 1. loop only if either of the files has a next line 1. a) do both files have next lines? -> compare file1, file2 and compare file1 , file2 + 1 and compare file1 + 1, file2 1. b) only file1 has a next entry, -> ADDED (I believe, or REMOVED, you know) 1. c) only file2 has a next entry, -> REMOVED (or the other way round ;))just 2. loop only if both files have next lines 2. a) == 1. a) just without the need to check if both have next 2. b) loop 2. a) ends, if none or only one of the files has one more entry. Now check if one of the two files has a line left and take care of that REMOVED or ADDED you've chosen for the more complex way 1. in 1. a) you checked for equality but did not do the additional checks if both files have next lines and if so, does one of the next lines match the actual line of the other file. Then you check for the end, that's OK again. I didn't check the code, just the logic.

Andrei

Level 41

9 February 2021, 13:49

I've been trying to understand your explanations for a few hours new, but I keep getting stuck at the between file1 and file2 + 1. I don't know how to get to that without and IndexOutOfBoundsException. I have rewritten the to what I believe would be a simpler version but I get stuck at line7 from file1 (there are so few lines left because I have written the loop to eliminate the lines after use - so I did that manually as well while running through the algorithm by hand to better understand how it works). Is this approach OK? Should I continue with this? Or should I try somehow else?

Andrei

Level 41

9 February 2021, 14:35

I have tweaked the block a bit more, it returns the correct result, but still doesn't verify so there must be an error in the algorithm logic.

while ( !LinesFile1.isEmpty() && !LinesFile2.isEmpty() ) {
            try { lineFile1 = LinesFile1.get(0); } catch (IndexOutOfBoundsException e) {break;}
            try { lineFile2 = LinesFile2.get(0); } catch (IndexOutOfBoundsException e) {break;}

            if (lineFile1.equals(lineFile2)) {
                lines.add(new LineItem(Type.SAME, lineFile1));
                LinesFile1.remove(0);
                LinesFile2.remove(0);
            }
            else {
                if (lineFile1.equals(LinesFile2.get(1))){
                    lines.add(new LineItem(Type.ADDED, lineFile2));
                    LinesFile2.remove(0);
                }
                    else {lines.add(new LineItem(Type.REMOVED, lineFile1));
                    LinesFile1.remove(0);}
            }
        }

Nouser

Level 36 , Germany

9 February 2021, 14:40

useful

some pseudo code, you should get the idea

String leftLine = itLeft.next();
String rightLine = itRight.next();

while (itLeft.hasNext() || itRight.hasNext()) {
    //there are now three possibilities when comparing left and right strings
    //1. left and right strings are equal
    if (leftLine.equals(rightLine)) {
        SAME;
        //however we do not know yet, if we can iterate left or right or left and right
        //1.1 we can iterate left and right, that's no problem, just do it
        if (itLeft.hasNext() && itRight.hasNext()) {
            leftLine = itLeft.next();
            rightLine = itRight.next();
        } else if (itLeft.hasNext()) {
            //1.2 there is just left a next value... means end of file is there
            REMOVED;
        } else if (itLeft.hasNext()) {
            //1.3 only the right side has a next value, advance right and add lo lines list
            ADDED;
        }
        //1.2 and 1.3 we advanced now on both sides to the end of the list
        //the next while loop iteration will end the loop cause no next lines are there
    } else if (lineEquals(leftLine, nextRightLine)) {
        //2. left and next line right are equal
        //we add a new LineItem to the lines list and iterate right, we can without check, done in equalsNextLine
        ADDED;
        rightLine = itRight.next();
    } else if (lineEquals(rightLine, nextLeftLine)) {
        //3. right and next line left are equal
        //we add a new LineItem to the lines list and iterate left, we can without check, done in equalsNextLine
        REMOVED;
        leftLine = itLeft.next();
    }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

9 February 2021, 14:42

"a reader, can it just read infinitely even after there are no more bytes to read?" Yes, a BufferedReader returns null for each read that is past the end of the data. With the original code it was reading from both files at the same time, only breaking when both files had all their lines read. This means that, most likely, one of the ArrayLists would have contained a few null values. The new code you shared with each reader having its own loop fixes this. Nouser's suggestion is good. You should try making the loop continue as long as each file has a next line. With your last post, you don't need try catch blocks at lines 2-3. If either file is empty then the loop will break and not IOOB Exception would occur here. Other than that, up to line 10 the code looks good. Your problem is line 11. If LinesFile2 has only one value in it, then trying to get the 2nd value (at index one) would throw an exception. You will need to ensure that there is an index 1 at that point before accessing it or the code crashes there. Also, what happens when that loop breaks and there are still additional values in one of the files?

Andrei

Level 41

9 February 2021, 15:37

OK, so I replicated your algorithm, Nouser, but it stops at line 4, even though, I ran through it multiple times and the logic is good.

String leftLine = bufferedReader1.readLine();
String rightLine = bufferedReader2.readLine();
String next;

while (bufferedReader1.ready() || bufferedReader2.ready()) {
    if (leftLine.equals(rightLine))
    {
        lines.add(new LineItem(Type.SAME, leftLine));
        if (bufferedReader1.ready() && bufferedReader2.ready())
        {
            leftLine = bufferedReader1.readLine();
            rightLine = bufferedReader2.readLine();
        }
        else if (bufferedReader1.ready())
        {
            lines.add(new LineItem(Type.REMOVED, bufferedReader1.readLine()));
        }
        else if (bufferedReader2.ready())
        {
            lines.add(new LineItem(Type.ADDED, bufferedReader2.readLine()));
        }
    }
    else if (leftLine.equals(next = bufferedReader2.readLine()))
    {
        lines.add(new LineItem(Type.ADDED, rightLine));
        rightLine = next;
    }
    else if (rightLine.equals(next = bufferedReader1.readLine()))
    {
        lines.add(new LineItem(Type.REMOVED, leftLine));
        leftLine = next;
    }
}

This is the output for the 2 full files: LineItem{SAME - line one is going to be the same} LineItem{REMOVED - line two is going to be removed} LineItem{SAME - line three is going to be the same}

Guadalupe Gagnon

Level 37 , Tampa, United States

9 February 2021, 18:38

useful

I had trouble with this problem too, and even my solution that passed is very complicated. It is not as hard as it seems though, you just need to take into consideration every possible scenario: a) The files are the same length b) file 1 is larger than file 2 c) file 2 is larger than file 1 So, a quick example of each: a) Both have 2 values line 1 - line 2 line 2 - line 3 (REMOVED, SAME, ADDED) b) File 1 is larger than file 2 line 1 - line 2 line 2 (REMOVED, SAME) c) File 2 is larger than file 1 line 2 - line 1 - line 2 (ADDED, SAME) This is going to be what determines how many times your main loop cycles. You need to account for any of these scenarios. In addition to that you will need to account for these scenarios at the end of the files: 1) the files both end with the same line 2) file 1 has an additional line at the end 3) file 2 has an additional line at the end Example: 1) both end with the same line (line 13) .... line 11 - line 12 line 12 - line 13 line 13 (REMOVED, SAME, SAME) 2) file 1 has an additional line (line 12) .... line 11 - line 11 line 12 (SAME, REMOVED) 3) file 2 has an additional line (line 12) .... line 11 - line 11 line 12 (SAME, ADDED) An edge case which you should consider, and I don't know if this task tests for it, is if either one of the files has 0 lines. If you work logically through these 6 points that edge case should naturally be caught, though lines 1-2 of the code shared right above this post would create problems as if there were no lines these would be set to null and crash the program at line 6 when leftLine.equals() is called.

Nouser

Level 36 , Germany

9 February 2021, 20:18

lines 14 and 19... you need to check, if there is a next line (I should have made that clear in my pseudo code) so read it like that ;)

} else if (lineEquals(leftLine, nextRightLineIfThereIsOne)) {

Andrei

Level 41

10 February 2021, 10:00

I have redone the code consider your feedback. I have also taken a look at the solution and adapted it from there as well. However, the output is still 3 lines: LineItem{SAME - line one is going to be the same} LineItem{REMOVED - line two is going to be removed} LineItem{SAME - line three is going to be the same} I don't understand why, because I have run multiple times through it and it doesn't make sense with it blocks at line 4.

while (bufferedReader1.ready() && bufferedReader2.ready()) {
            if (leftLine.equals(rightLine))
            {
                lines.add(new LineItem(Type.SAME, leftLine));
                leftLine = bufferedReader1.readLine();
                rightLine = bufferedReader2.readLine();
            }
            else if (bufferedReader2.ready() && leftLine.equals(next = bufferedReader2.readLine()))
                {
                    lines.add(new LineItem(Type.ADDED, rightLine));
                    rightLine = next;
                }
            else if (bufferedReader1.ready() && rightLine.equals(next = bufferedReader1.readLine()))
                {
                    lines.add(new LineItem(Type.REMOVED, leftLine));
                    leftLine = next;
                }

            }

        while (bufferedReader1.ready()) {
            lines.add(new LineItem(Type.REMOVED, bufferedReader1.readLine()));
        }

        while (bufferedReader2.ready()){
            lines.add(new LineItem(Type.ADDED, bufferedReader2.readLine()));
        }

Nouser

Level 36 , Germany

10 February 2021, 11:22

solution

you're skipping lines in line 8 if the if-else clause is false. leftLine.equals(next = bufferedReader2.readLine())) file1line1 file2line1 file1line2 file2line2 it's like file1line1 == file2line2 -> false do nothing... and do the next check file1line2 == file2line1 but the file pointer of both files advanced to the next line and not just the intended of the last check Easy to fix if you're using lists. If you're comparing the files directly you could read 2 lines at once file1line1 file2line1 file1line2 file2line2 you need strings for these 4 options. Then you cn step back again if needed.

Andrei

Level 41

10 February 2021, 11:46

Thanks, I finally did it on my 30th attempt, but, not gonna lie, I'm not satisfied with the way it went. Based on your recommendations I just ended up doing like in the solution provided by the Mentor. Oh well. Thanks a lot for both of your input, I greatly appreciate it. I have deepened my knowledge after this exercise even though it did not come out as I'd wished.