CodeGym/Help with Java Tasks/Help is greatly appreciated

Level 22

10.11.2020
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Help is greatly appreciated

Question about the task

Under discussion

I'm failing the last condition..

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.IOException; import java.io.InputStreamReader; import java.util.*; /* Tracking changes */ public class Solution { public static List<LineItem> lines = new ArrayList<>(); public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String file1 = reader.readLine(); String file2 = reader.readLine(); reader.close(); BufferedReader file1Reader = new BufferedReader(new FileReader(file1)); BufferedReader file2Reader = new BufferedReader(new FileReader(file2)); ArrayList<String> file1List = new ArrayList<>(); ArrayList<String> file2List = new ArrayList<>(); String line; while ((line = file1Reader.readLine()) != null) { file1List.add(line); } file1Reader.close(); while ((line = file2Reader.readLine()) != null) { file2List.add(line); } file2Reader.close(); ArrayList<String> mergedList = new ArrayList<>(file1List); for (String s : file2List) { if (!mergedList.contains(s)) { mergedList.add(s); } } TreeMap<String, Type> ordered = new TreeMap<String, Type>(); for (String s : mergedList) { if (file1List.contains(s) && file2List.contains(s)) { if (!ordered.containsKey(s)) { ordered.put("SAME " + s, Type.SAME); } } if (file1List.contains(s) && !file2List.contains(s)) { if (!ordered.containsKey(s)) { ordered.put("REMOVED" + s, Type.REMOVED); } } if (!file1List.contains(s) && file2List.contains(s)) { if (!ordered.containsKey(s)) { ordered.put("ADDED" + s, Type.ADDED); } } } for (Map.Entry<String, Type> entry : ordered.entrySet()) { lines.add(new LineItem(entry.getValue(), entry.getKey())); } } 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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Guadalupe Gagnon

Level 37 , Tampa, United States

10 November 2020, 15:47

#1The mergedList would need to be in exact order to solve this task. Right now it adds all the lines from file 1, then the lines that are added from file2 are added to the very end of the list (out of the correct order). I don't see how you could accomplish ordering them separately from figuring out which lines match, are removed, or are added. This means that to create this list you would first have to successfully solve the task, making it redundant to then use this list to solve the task a second time. See my post on the task page for example inputs. I used those and this was the output of the list was: LineItem{ADDED - ADDEDline eight is going to be added} LineItem{ADDED - ADDEDline six is going to be added} LineItem{REMOVED - REMOVEDline four is going to be removed} LineItem{REMOVED - REMOVEDline two is going to be removed} LineItem{SAME - SAME line five is going to be the same} LineItem{SAME - SAME line nine is going to be the same} LineItem{SAME - SAME line one is going to be the same} LineItem{SAME - SAME line seven is going to be the same} LineItem{SAME - SAME line three is going to be the same} The correct output would have the numbers in the correct order one-nine #2 The code should not be adding SAME, REMOVED, ADDED to the String literals. Those lines above should read: LineItem{ADDED - line eight is going to be added} LineItem{ADDED - line six is going to be added} LineItem{REMOVED - line four is going to be removed} etc You can get this by adding a toString() method to the LineItem class:

public String toString() {
   return "LineItem{" + type + " - " + line + "}";
}

Seferi

Level 22 , United Federation of Planets

10 November 2020, 19:49

Thanks for replying mate. I thought the 'TreeMap ordered' would put the items in order because the Strings have numbers in them, line1, line2 etc... But I'm guessing this is not the case.. The conditions are pretty misleading here... But if the String doesn't have line numbers on it and there are no empty lines on both files, how are we going to know which line is which.. I don't get it...

Seferi

Level 22 , United Federation of Planets

10 November 2020, 20:34

I edited the code a bit, as much as I understood.. Still doesn't work...

public class Solution {
    public static List<LineItem> lines = new ArrayList<>();

    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String file1 = reader.readLine();
        String file2 = reader.readLine();
        reader.close();

        BufferedReader file1Reader = new BufferedReader(new FileReader(file1));
        BufferedReader file2Reader = new BufferedReader(new FileReader(file2));
        ArrayList<String> file1List = new ArrayList<>();
        ArrayList<String> file2List = new ArrayList<>();
        String line;

        while ((line = file1Reader.readLine()) != null) {
            file1List.add(line);
        }
        file1Reader.close();
        while ((line = file2Reader.readLine()) != null) {
            file2List.add(line);
        }
        file2Reader.close();

        for (int i = 0; i < file2List.size(); i++) {
            if (file1List.get(i).equals(file2List.get(i))) {
                lines.add(new LineItem(Type.SAME, file1List.get(i)));
            }
            else if (!file2List.contains(file1List.get(i))) {
                lines.add(new LineItem(Type.REMOVED, file1List.get(i)));
            }
            else if (!file1List.contains(file2List.get(i))) {
                lines.add(new LineItem(Type.ADDED, file2List.get(i)));
            }
        }
    }

    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;
        }
    }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

10 November 2020, 21:21

Line1, line2, line3 is not what would be in the file. The file would contain something like a book, maybe like Moby Dick. Basically they can contain anything, and like a book, wont be in alphabetic order. The thing is that the second file is an updated version of the first file and your code has to take each and figure out the updates are. There is one restriction that codegym makes of the test files: When an item is ADDED or REMOVED, then the next line will absolutely be SAME. In the code shared directly above, lines 25-35 would not work. Take for example when you have file1 values: To be or not to be that is the question? and file2 contained: that is the question? Whether 'tis nobler in the mind to suffer The correct input into the lines array would be: "To be or not to be" - REMOVED "that is the question?" - SAME "Whether 'tis nobler in the mind to suffer" - ADDED The problem with that code is the only counter is i. When i equals 0: file1List.get(0) = "To be or not to be" file2List.get(0) = "that is the question?" when i equals 1: file1List.get(1) = "that is the question?" file2List.get(1) = "Whether 'tis nobler in the mind to suffer" Neither of these match and so line 26 wouldn't return true, and because "that is the question?" is in both files lines 29 and 32 would both be false on these lines and never be added to the lines list.

Seferi

Level 22 , United Federation of Planets

11 November 2020, 11:58

But that's why I used 'contains'.. !file1List.contains(file2List.get(i) if the file1List doesn't contain file2.get(i). So it's not comparing file1List.get(i) and file2List.get(i) but just checking if it contains it... I changed the if else to ifs.. I still don't get it why it wouldn't work... Why it at least doesn't some lines in lines... :(

Seferi

Level 22 , United Federation of Planets

11 November 2020, 12:50

Just realized my line readers don't work at all... :/

Guadalupe Gagnon

Level 37 , Tampa, United States

11 November 2020, 14:30

"But that's why I used 'contains'.." Technically you used DOES NOT contain, and that it a problem when using only one index counter. The lines in the file won't match exactly as each file will contain lines that the other does not. This means that the amount of lines in each file wont be the same, and can be wildly off. Take for example 2 files where file2 adds no new lines but subtracts 6 lines from the main. So the first file would would have 12 lines while the second file would would have 6: so file1 would have: and file 2 would have line 1 line 2 line 2 line 4 line 3 line 6 line 4 line 8 line 5 line 10 line 6 line 12 line 7 line 8 line 9 line 10 line 11 line 12 The correct output for this example would be: line 1 - REMOVED line 2 - SAME line 3 - REMOVED line 4 - SAME line 5 - REMOVED line 6 - SAME line 7 - REMOVED line 8 - SAME line 9 - REMOVED line 10 - SAME line 11 - REMOVED line 12 - SAME Your code wouldn't work for this. It first would never find a SAME in these two lists because using the same index to access values there isn't a single value that equals the one at the same index in the other file. Problem 2 is because you use file2.size() as the condition that runs the loop, it would end when i equals 6, meaning in my example that indices 6-11 of the first list would never be considered.

Seferi

Level 22 , United Federation of Planets

11 November 2020, 15:15

Yes, I realized that with the fileList.size()... Thanks for the through explanation mate. In your last example if I go through the file1 with a for loop and do if 'file2.contains(line)' it would add line - SAME right ? (because both files has the line) And any ideas why my linereader doesn't work at all?

while ((line = file1Reader.readLine()) != null) {
            file1List.add(line);
        }
        file1Reader.close();

Guadalupe Gagnon

Level 37 , Tampa, United States

11 November 2020, 15:29

Are you sure its your file reader? The code looks good to me. The only thing I would mention, and this doesn't mean that your code is wrong, but whenever you are reading from a source that has a definite end point, such as a file, a more proper way to use the BufferedReader would be:

while(reader.hasNext()){
     // read data
}

The way you do it is the better way when there is no definite end point, such as accepting user data until they enter a stop condition. "In your last example if I go through the file1 with a for loop and do if 'file2.contains(line) it would add line - SAME right ?" Yes, however now you would need to consider the case where file1 had only 6 lines and file2 had 12 (meaning all the lines are ADDED instead of REMOVED). Using only file1 in that case wouldn't work for the same reason going through only file2 doesn't work for my last example.

Seferi

Level 22 , United Federation of Planets

27 November 2020, 19:53

Hi, most of the code is the same, I'm having trouble with the last line and can't seem to find a solution. Added an extra line to the list which probably will cause problems too. And as it is, it doesn't work if the last line is ADDED...

String line;

while ((line = file1Reader.readLine()) != null) {
    file1List.add(line);
}
file1List.add(" ");
file1Reader.close();
while ((line = file2Reader.readLine()) != null) {
    file2List.add(line);
}
file2List.add(" ");
file2Reader.close();
int index1 = 0;
int index2 = 0;
while (index1 != file1List.size() - 1) {
    if (file1List.get(index1).equals(file2List.get(index2))) {
        lines.add(new LineItem(Type.SAME, file1List.get(index1)));
        index1++;
        index2++;
        continue;
    }
    if (!file1List.get(index1).equals(file2List.get(index2)) && file1List.get(index1 + 1).equals(file2List.get(index2))) {
        lines.add(new LineItem(Type.REMOVED, file1List.get(index1)));
        index1++;
    } else {
        lines.add(new LineItem(Type.ADDED, file2List.get(index2)));
        index2++;
    }
}

Guadalupe Gagnon

Level 37 , Tampa, United States

27 November 2020, 20:26

what if the files had data like this? file1 : file 2: line 2 line 1 line 3 line 2 line 3 line 4 Line 15 of this code only goes as long as the index of the file1 contents is not at the end. If the files contained this data then the loop would break early and not add "line 4" from file 2.