How to load parts of a file using jFrame into an ArrayList in Java?

Question

I am writing a program for an assignment that uses a jFrame UI to read the contents of a notepad file full of "grades" (A, B, C, C+ etc) and then calculate the total number of grades, and the highest and lowest grades. In the jFrame, the user inputs a file name (I do not want to use JFileChooser because that is not part of the assignment) and clicks "load" to load the file. I am struggling with the Load() method. So far, I have:

  public ArrayList<LetterGrade> Load(File file) throws FileNotFoundException {

    ArrayList<LetterGrade> grades = new ArrayList();

    try{
        Scanner input = new Scanner(file);
        String grade = input.nextLine();
        grades.add(LetterGrade.grade);
    } catch (FileNotFoundException ex) {
        System.out.printf("ERROR: %s", ex);
    }

    return grades;

I know that there is a problem in the line that says grades.add(LetterGrade.grade) because I can only add a LetterGrade enum (A, AMinus, BPlus, B etc) to the ArrayList "grades" whereas grade is a String. How can I make it so that when Scanner reads the file, it takes each grade and adds it to the ArrayList called "grades"? Also, I only want to take grades that are part of my LetterGrade enum, so would I use an if/else to filter that? Thanks for the help, and I will respond as quickly as possible to questions.

Answer 1

Java isn't able to automatically convert a String with the value of a LetterGrade directly into a LetterGrade . You can write that function yourself. Try doing something like this:

LetterGrade parseGrade(String grade) {
    if(grade.equals("A") return LetterGrade.A;
    // and so on
}

And then, instead of

grades.add(LetterGrade.grade);

in Load() , you would have this:

grades.add(parseGrade(grade));

If you want to check that what you're adding is a valid grade first, have parseGrade() return null if it's an invalid grade, then check for null while adding the grade to grades .

Answer 2

Change LetterGrade.grade to

LetterGrade.valueOf(grade);

LetterGrade.grade would be used to access a variable named grade in the scope of LetterGrade.

You need to convert the String to Enum.

See Lookup enum by string value for more detials