Abstracting Java Strings data from ArrayList and manipulating it using I/O files

I am a beginner. I am trying to learn 1) Read data from a file and store inside ArrayList 2) Manipulate String data 3) Output results to a new file using ArrayList. I have figured out Part 1 and Part 3 and I have provided the code. I am having problems manipulating strings. I am sure there is an easier solution but I am not able to see it even after spending many hours. I know I need to use either charAt(i) or note.substring() or both. Maybe a nested loop?

// Part 1 Reading notes from a file and storing it into ArrayList named list.
    BufferedReader bufReader = new BufferedReader(new FileReader("read1.txt"));
    List<String> list = new ArrayList<>();
    String line = bufReader.readLine();
    while (line != null) {
        list.add(line);
        line = bufReader.readLine();
    }
    bufReader.close();
    list.forEach(System.out::println);//Print list to the Screen

    read1.txt  file   
    E  F#G# F#G# E   EF#D# E C#    E D# C# BB  C#C#
    C# E F# G# G# BAAG#   C# E F# G# C# B A G#

    May have lyrics here which needs to be avoided
    C# E G# C# B A G# G# B A G# F# A F# B G# F# D#

PART 2 This is where I'm having a problem. list[0] has many different musical notes with and without #. How do I sperate each note with "," so result would look something like following. I want to keep the format same. I don't want to remove the whitespaces.

    E,  F#,G#, F#,G#, E,   E,F#,D#, E, C#,    E, D#, C#, B,B,  C#,C#
    C#, E, F#, G#, G#, B,A,A,G#,   C#, E, F#, G#, C#, B, A, G#,

    May have lyrics here which needs to be avoided
    C#, E, G#, C#, B, A, G#, G#, B, A, G#, F#, A, F#, B, G#, F#, D#

I want to store above result into another ArrayList named printToFile and I want to output the result using following code.

//PART 3 This code will write List to a desired new file(write2.txt)
    List<String> printToFile = new ArrayList<>();
    //here We are assuming that results have been populated into printToFile
    BufferedWriter bufWriter = new BufferedWriter(new FileWriter("write2.txt"));

    for (String wline : printToFile) {
        bufWriter.write(wline);
        bufWriter.newLine();
    }
    bufWriter.close();

Can someone pls teach me how to do Part2. I have tested Part1 and Part3. They work. For me, this is a learning tutorial so I will WELCOME different suggestions and ideas. Thanks

You may try replaceAll with a regular expression to replace each note [A-G] followed by optional # and removing trailing comma:

String line = "E  F#G# F#G# E   EF#D# E C#    E D# C# BB  C#C#";
String str = line.replaceAll("([A-G]#?)", "$1,");
if (str.endsWith(",")) {
    str = str.substring(0, str.length() - 1);
}
System.out.println(line);
System.out.println(str);

Output:

E  F#G# F#G# E   EF#D# E C#    E D# C# BB  C#C#
E,  F#,G#, F#,G#, E,   E,F#,D#, E, C#,    E, D#, C#, B,B,  C#,C#

note: if the input data contain other types of notes flat or sharp, the regular expression needs to be updated accordingly.

update<br/>
More advanced regular expression enables proper insertion of commas after each note except the last one (without removal of the trailing comma with additional code).

String str2 = line.replaceAll("([A-G]#?+(?!$))", "$1,");
System.out.println(str2);

([A-G]#?+(?!$)):

• 1st Capturing Group ([A-G]#?+(?!$))
  • Match a single character present in the list below [A-G]<br/>
    A-G a single character in the range between A (index 65) and G (index 71) (case sensitive)
  • #?+ matches the character # literally (case sensitive)<br/>
    ?+ Quantifier — Matches between zero and one times, as many times as possible, without giving back (possessive)
  • Negative Lookahead (?!$)<br/>
    Assert that the Regex below does not match<br/>
    $ asserts position at the end of a line

online demo

It also may be needed to verify if the given input string looks like a string of notes and then apply this modification to avoid inserting commas after single-letter words which might happen in the lyrics.

The matching regular expression is: ^(\s*[A-G]#?\s*)+$ - it checks if there is at least one note surrounded with optional whitespaces \s*.

So, the final solution would look like:

private static String insertCommasIfLineOfNotes(String line) {
    if (null == line || !line.matches("^(\\s*[A-G]#?\\s*)+$")) {
        return line;
    }
    return line.replaceAll("([A-G]#?+(?!$))", "$1,");
}

// test
List<String> lines = Arrays.asList(
        "E  F#G# F#G# E   EF#D# E C#    E D# C# BB  C#C#", 
        "A Perfect Day Elise",
        "A B C D E F G H I J K L M N O P"
);
lines.stream()
     .map(MyClass::insertCommasIfLineOfNotes)
     .forEach(System.out::println);

// output
E,  F#,G#, F#,G#, E,   E,F#,D#, E, C#,    E, D#, C#, B,B,  C#,C#
A Perfect Day Elise
A B C D E F G H I J K L M N O P

update 2<br/>
If it is needed to get a list of substrings in the line of notes, containing plain notes A..G optionally followed by #, or sequences of 1 or more whitespaces, the following methods can be implemented.<br/>
refactored to add whitespace sequences to appropriate note entry to facilitate joining of the notes into single string

private static List<String> buildListOfNotes(String line) {
    if (null == line || !line.matches("^(\\s*[A-G]#?\\s*)+$")) {
        return Arrays.asList(line); // for lyrics line
    }
    List<String> result = new ArrayList<>();
      
    int spaceStart = -1;
    int spaceEnd = 0;
    for(int i = 0; i < line.length() - 1; i++) {
        char c = line.charAt(i);
        boolean note = isNote(c);
        
        if (isNote(c)) {
            String prefix = "";
            if (spaceStart > -1) {
                // add existing whitespace as a prefix to current note
                int prevResult = result.size() - 1;
                prefix = line.substring(spaceStart, spaceEnd);
                spaceStart = -1;
            }
            if (line.charAt(i + 1) == '#') {
                result.add(prefix + line.substring(i, i + 2));
                i++;
            } else {
                result.add(prefix + line.substring(i, i + 1));
                if (!isNote(line.charAt(i + 1))) {
                    spaceStart = i + 1;
                }
            }
        } else {
            if (spaceStart == -1) {
                spaceStart = i;
                spaceEnd = i + 1;
            } else {
                spaceEnd++;
            }
        }
      }
      if (spaceStart > -1) {
          // add trailing whitespace if available to the last note
          int prevResult = result.size() - 1;
          result.set(prevResult, result.get(prevResult) + line.substring(spaceStart));
      }
      return result;
  }
  
  private static boolean isNote(char c) {
      return c >= 'A' && c <= 'G';
  }

// testing method to retrieve list of substring
List<String> lines = Arrays.asList(
        "E  F#G# F#G# E   EF#D# E C#    E D# C# BB  C#C#",
        "E  F#G# F#G# E   EF#D# E C#    E D# C# BB  C#C#    ",
        "   E  F#G# F#G# E   EF#D# E C#    E D# C# BB  C#C",
        "   E  F#G# F#G# E   EF#D# E C#    E D# C# BB  C#C ", 
        "A Perfect Day Elise",
        "A B C D E F G H I J K L M N O P"
);
lines.stream()
     .map(MyClass::buildListOfNotes)
     .forEach(System.out::println);

Test output ("note" entry may include whitespace sequence):

[E,  F#, G#,  F#, G#,  E,   E, F#, D#,  E, C#,     E, D#,  C#,  B, B, C#, C#]
[E,  F#, G#,  F#, G#,  E,   E, F#, D#,  E, C#,     E, D#,  C#,  B, B, C#, C#    ]
[   E,  F#, G#,  F#, G#,  E,   E, F#, D#,  E, C#,     E, D#,  C#,  B, B, C#]
[   E,  F#, G#,  F#, G#,  E,   E, F#, D#,  E, C#,     E, D#,  C#,  B, B, C#, C ]
[A Perfect Day Elise]
[A B C D E F G H I J K L M N O P]

Then the array of notes can be easily converted into String using String.join:

// lineToWrite will contain original whitespaces
String lineToWrite = String.join(",", buildListOfNotes(line));

// cleanLine will contain notes without extra spacing
String cleanLine = buildListOfNotes(line).stream()
                                         .map(String::trim)
                                         .collect(Collectors.joining(", "));

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