Reading/splitting different parts from different lines in a text file in Java

Question

I'm working on this assignment I'm supposed to read from a text file like this...

Student Name: John
Student ID: 12344/19
College: Science

Credits Attempted: 15
Credits Earned: 15
Grade Points: 41.2
Course Code Course Title            Credit      Grade
COMP1007,   Amazing Applications of AI,  2,      B
COMP2202,   Fund. of Object Oriented Prog.,  3,      C-
MATH2108,   Calculus (2),            3,          C-
MATH3340,   Discrete Math. for Comp. Sci.,   3,          B-
STAT2101,   Introduction to Statistics,      4,          C+

I should read this text file and calculate the GPA of the student and create an output file that should look like this...

Output text file

So basically I'm stuck and I have no idea what I to do... I know how to read line by line and split a line into different parts, but this doesn't seem to work here since every line is different from the other. For example the first line has two parts, the "Student Name" and the name itself in this case "John". But in line 9, there are four different parts, the course code, course name, credit and grade.

I'm honestly not looking to cheat on the assignment but only to understand it

help :)

Note I can't use Stream or Hashmap or BufferedReader

Answer 1

OK, so here's how you do it ...

1. You read in all of the file and store each line in a List<String>
2. For the first 8 lines you process each one in a separate way. You can even write a separate function to parse the necessary info out of every line for lines 0-7
3. All the remaining lines have identical structure. Therefore, you can process them all in the same way to parse out and then process the necessary data.

And a comment to this answer if something is unclear and I'll clarify.

Answer 2

Each data record in a text file always has a Start and an End . The easiest records are obviously those that are contained on a single delimited line within the text file, where each file line is in fact a record as you can see within a typical CSV format data file. The harder records to read are the Multi-Line records whereas each data record consists of several sequential text file lines but still, there is a Start and a End to each record.

The Start of a record is usually pretty easy to distinguish. For example, in the file example you provided in your post it is obviously any file line that starts with Student Name: .

The End of a record may not always be so easy to determine since many applications do not save fields which contain no data value in order to help increase access speed and reduce file bloat. The thought is "why have a text file full of empty fields" and to be honest, rightly so. I'm not a big fan of text file records anyways since utilizing a database would make far better sense for larger amounts of data. In any case, there will always be a file line that will indicate the Start of a record so it would make sense to read from Start to Start of the next record or in the case of the last record in file, from Start to End Of File (EOF).

Here is an example (read the comments in code):

// System line separator to use in files.
String ls = System.lineSeparator();   
/* Array will hold student data: Student Name, Student ID, College,
   Credits Attempted, Credits Earned, and finally Grade Points.  */
String[] studentData = new String[6]; 
// String Array to hold Course Table Header Names.
String[] coursesHeader = {"COURSE NO", "COURSE TITLE", "CREDITS", "GRADE"};
// List Interface to hold all the course Data line Arrays for each record
java.util.List<String[]> cousesList = new java.util.ArrayList<>();
// Underlines to be used for Console display and file records
// Under courses Header
String underline1 = "-------------------------------------------------------------";
// Under all the courses
String underline2 = "------------------------------------------------------------------------------------";
    
/* Read and Write to files using 'Try With Resources' so to 
   automatically close the reader an writer objects.     */
try (Scanner reader = new Scanner(new java.io.File("StudentData.txt"), "UTF-8"); 
            java.io.Writer writer = new java.io.FileWriter("StudentsGPA.txt")) {
    // For console display only! [Anything (except caught errors) to Console can be deleted]
    System.out.println("The 'StudentsGPA.txt' file will contain:");
    System.out.println("======================================");
    System.out.println();
        
    // Will hold each line read from the reader
    String line = "";
    /* Will hold the name for the next record. This would be the record START
       but only AFTER the first record has been read.          */
    String newName = "";
        
    // Start reading the 'StudentData.txt' file (line by line)...
    while (reader.hasNextLine()) {
        /* If newName is empty then we're on our first record or 
           there is only one record in file.             */
        if (newName.isEmpty()) {
            line = reader.nextLine();   // read in a file line...
        }
        else {
            /* newName contains a name so we must have bumped into
               the START of a new record during processing of the 
               previous record. We aleady now have the first line 
               of this new record (which is the student's name line) 
               currently held in the 'newName' variable so we just 
               make 'line' equal what is in the 'newName' variable
               and carry on processing the data as normal. in essance,
               we simply skipped a read because we've already read it 
               earlier when processing the previous record.    */
            line = newName;
            // Clear this variable in preparation for another record START.
            newName = "";  
        }
        /* Skip comment lines (lines that start with a semicolon (;)
           or a hash mark (#). Also skip any blank lines.            */
        if (line.startsWith(";") || line.startsWith("#") || line.isEmpty()) {
            continue;
        }
        /* Does this file line start with 'Student Name:'? If so then 
           this is a record START, let's process this record. If not 
           then just keep reading the file.            */
        if (line.startsWith("Student Name:")) {
            /* Let's put the student name into the studentData array at 
               index 0. If it is detected that there has been no name
               applied for some reason then we place "N/A" as the name.
               We use a Ternary Operator for this. So, "N/A" will be a 
               Default if there is not name. This will be typical for 
               the other portions of student data.                */
            studentData[0] = line.isEmpty() ? "N/A" : line.split("\\s*:\\s*")[1].trim();
            /* Let's keep reading the file from this point on and retrieve 
               the other bits of student data to fill the studentData[] 
               Array...                    */
            for (int i = 1; i < 6; i++) {
                line = reader.nextLine().trim();
                /* If we encounter a comment line or a blank line then let's
                   just skip past it. We don't want these.               */
                if (line.startsWith(";") || line.startsWith("#") || line.isEmpty()) {
                    i--;
                    continue;
                }
                /* Store the other portions of student data into the 
                   studentData Array using "N/A" as a default should
                   any student data field contain nothing.        */
                studentData[i] = line.isEmpty() ? "N/A" : line.split("\\s*:\\s*")[1].trim();
            }
            // The current Student's Courses...
            /* Clear the List Interface object in preparation for new 
               Courses from this particular record.               */
            cousesList.clear();
            // Read past the courses header line...We don't want it.
            reader.nextLine();
            // Get the courses data (line by line)...
            while (reader.hasNextLine()) {
                line = reader.nextLine().trim();
                /* Again, if we encounter a comment line or a blank line 
                   in this section then let's just skip past it. We don't 
                   want these. */
                if (line.startsWith(";") || line.startsWith("#") || line.isEmpty()) {
                    continue;
                }
                /* At this point, if we have read in a line that starts
                   with 'Student Name:' then we just hit the START of a 
                   NEW Record! This then means that the record we're 
                   currently working on is now finished. Let's store this 
                   file line into the 'newRecord' variable and then break 
                   out of this current record read.                     */
                if (line.startsWith("Student Name:")) {
                    newName = line;
                    break;
                }
                /* Well, we haven't reached the START of a New Record yet
                   so let's keep creating the courses list (line by line). 
                   Break the read in course line into a String[] array.
                   We use the String#split() method for this with a small
                   Regular Expression (regex) to split each line based on
                   comma delimiters no matter how the delimiter spacing 
                   might be (ex: ","  " ,"  " , " or even "      ,   ").  */
                String[] coursesData = line.split("\\s*,\\s*");
                /* Add this above newly created coursesData string array 
                   to the list.   */
                cousesList.add(coursesData);
            }
            /* Write (append) this current record to new file. The String#format()
               method is used here to save the desired data into the 'StudentGPA.txt'
               file in a table style format.            */
            // Student Data...
            writer.append(String.format("%-12s: %-25s", "ID", studentData[1])).append(ls);
            writer.append(String.format("%-12s: %-25s", "Name", studentData[0])).append(ls);
            writer.append(String.format("%-12s: %-25s", "College", studentData[2])).append(ls);
            // Student Courses...
            // The Header line
            writer.append(String.format("%-13s %-30s %-10s %-4s", coursesHeader[0], 
                          coursesHeader[1], coursesHeader[2], coursesHeader[3])).append(ls);
            // Apply an Underline (underline1) under the header.
            writer.append(underline1).append(ls);
            // Write the Courses data in a table style format to make the Header format.
            for (String[] cData : cousesList) {
                writer.append(String.format("%-13s %-33s %-9s %-4s", 
                              cData[0], cData[1], cData[2], cData[3])).append(ls);
            }
            // Apply an Underline (underline2) under the Courses table.
            writer.append(underline2).append(ls);
                                    
            // Display In Console Window (you can delete this if you want)...
            System.out.println(String.format("%-12s: %-25s", "ID", studentData[1]));
            System.out.println(String.format("%-12s: %-25s", "Name", studentData[0]));
            System.out.println(String.format("%-12s: %-25s", "College", studentData[2]));
            System.out.println(String.format("%-13s %-30s %-10s %-4s", coursesHeader[0],
                               coursesHeader[1], coursesHeader[2], coursesHeader[3]));
            System.out.println(underline1);
            for (String[] cData : cousesList) {
                System.out.println(String.format("%-13s %-33s %-9s %-4s", 
                                    cData[0], cData[1], cData[2], cData[3]));
            }
            System.out.println(underline2);
                
            // The LAST line of each record, the Credits...
            // YOU DO THE CALCULATIONS FOR: totalAttemped, semGPA, and cumGPA
            String creditsAttempted = studentData[3];
            String creditsEarned = studentData[4];
            int credAttempted = 0;
            int credEarned = 0;
            int totalAttempted = 0;
            double semGPA = 0.0d;
            double cumGPA = 0.0d; 
            /* Make sure the 'credits attemted' numerical value is in fact 
               a string representaion of an integer value. if it is then
               convert that string numerical value to integer.  */
            if (creditsAttempted.matches("\\d+")) {
                credAttempted = Integer.valueOf(creditsAttempted);
            }
            /* Make sure the 'credits earned' numerical value is in fact 
               a string representaion of an integer value. if it is then
               convert that string numerical value to integer.  */
            if (creditsEarned.matches("\\d+")) {
                credEarned = Integer.valueOf(creditsEarned);
            }
            // Build the last record line (the Credits string) with the acquired data.
            String creditsString = new StringBuilder("CREDITS: TOTAL.ATTEMPTED ")
                    .append(totalAttempted).append("? EARNED ").append(credEarned)
                    .append(" ATTEMPTED ").append(credAttempted).append("  SEM GPA   ")
                    .append(semGPA).append("?   CUM GPA   ").append(cumGPA).append("?")
                    .toString();
            // Display it to the console Window (you can delete this).
            System.out.println(creditsString);
            System.out.println();
                
            // Write the built 'credit string' to file which finishes this record.
            writer.append(creditsString).append(ls);
            writer.append(ls);  // Blank Line in preparation for next record.
            writer.flush();     // Flush the data buffer - write record to disk NOW.
        }
    }
}
// Trap Errors...Do whatever you want with these.
catch (FileNotFoundException ex) {
    System.err.println("File Not Found!\n" + ex.getMessage());
}
catch (IOException ex) {
    System.err.println("IO Error Encountered!\n" + ex.getMessage());
}

Yes, it looks long but if you get rid of all the comments you can see that it really isn't. Don't be afraid to experiment with the code. Make it do what you want.

---

EDIT: (as per comments)

To place the student info portion of each record into an ArrayList so that you can parse it the way you want:

Where the for loop is located within the example code above for gathering the student info, just change this loop to this code and parse the data the way you want:

// Place this ArrayList declaration underneath the 'underline2' variable declaration:
java.util.ArrayList<String> studentInfo = new java.util.ArrayList<>();

then:

if (line.startsWith("Student Name:")) {
    studentInfo.clear();
    studentInfo.add(line);
    /* Let's keep reading the file from this point on and retrieve 
       the other bits of student data to fill the studentData[] 
       Array...                      */
    for (int i = 1; i < 6; i++) {
        line = reader.nextLine().trim();
        /* If we encounter a comment line or a blank line then let's
           just skip past it. We don't want these.          */
        if (line.startsWith(";") || line.startsWith("#") || line.isEmpty()) {
            i--;
            continue;
        }
        studentInfo.add(line);
    }
    
    // .................................................
    // .... The rest of the code for this `if` block ...
    // .................................................
}

You will of course need to change the code after this loop to properly represent this ArrayList.