从文件读入并添加到2D数组

Question

I have two different programs, one which contains a method "addGrade" designed to add a new grade to a 2D array (gradeTable). One array of the 2D array is the category each grade should be in, and the second element is the grades for each category. Here is that program:

public class GradeBook {


private String name;
private char[] categoryCodes;
private String[] categories;
private double[] categoryWeights;
private double[][] gradeTable;

public GradeBook(String nameIn, char[] categoryCodesIn, 
  String[] categoriesIn, double[] categoryWeightsIn) {

  name = nameIn;
  categoryCodes = categoryCodesIn;
  categories = categoriesIn;
  categoryWeights = categoryWeightsIn;
  gradeTable = new double[5][0];
}

public boolean addGrade(String newGradeIn) {     

  char row = newGradeIn.charAt(0);
  int grade = Integer.parseInt(newGradeIn.substring(1));

  double[] oldArr = gradeTable[row];
  double[] newArr = Arrays.copyOf(oldArr, oldArr.length + 1);
  newArr[newArr.length - 1] = grade;
  gradeTable[row] = newArr;

  return row != 0; 
}

The second program reads in a file as a command argument. The bolded text represents the grades being read in. The letter stands for that category each grade should be in, and the number is the actual grade. The file is

Student1  
5  
a Activities 0.05  
q Quizzes 0.10  
p Projects 0.25  
e Exams 0.30  
f Final 0.30  
**a100 a95 a100 a100 a100  
q90 q80 q100 q80 q80 r90  
p100 p95 p100 p85 p100  
e77.5 e88  
f92**  

In the second program, I'm trying to loop through each grade in the file and call the addGrade method on it so it will be added to the 2D array. I'm unsure of how to call the method for each individual grade. Also, I'm pretty sure my addGrade method isn't right. Any help would be appreciated. This is the second program:

public class GradeBookApp {

  String fileName = "";
  String name = "";
  char[] categoryCodes = new char[5];
  String[] categories = new String[5];
  double[] categoryWeights = new double[5];
  double[][] gradeTable;


  if (args.length > 0) {

     for (int i = 0; i < args.length; i++) {
        System.out.println("Reading file \"" + args[i] + "\"." 
           + "\n\tCreating GradeBook object."
           + "\n\tAdding grades to GradeBook object."
           + "\nProcessing of file complete.");


        fileName = args[i];
        Scanner scanFile = new Scanner(new File(fileName));

        name = scanFile.nextLine();
        int catCodes = Integer.parseInt(scanFile.nextLine());

        for (i = 0; i < catCodes; i++) {
           String[] all = scanFile.nextLine().split(" ");
           if(all.length == 3 && all[0].length() == 1 && all[2].matches("(\\d+\\.\\d+)")){
              categoryCodes[i] = all[0].charAt(0);
              categories[i] = all[1];
              categoryWeights[i] = Double.parseDouble(all[2]);
           }
        }

        GradeBook myGB = new GradeBook (name, categoryCodes, 
           categories, categoryWeights);

Answer 1

You'd be better off with having each list of grades as an ArrayList<Double> rather than a double[] . It's very hard work on the JVM (and on the programmer!) having to copy the whole array each time so that you can increase its length and add a new one. If you use an ArrayList<Double> gradeList , then you can just

gradeList.add(grade);

without needing to do all the copying.

I would also consider having the larger structure as a Map rather than an array. So rather than having a two-dimensional array, you could have a HashMap<Character,List<Double>> that maps the row onto the list of grades for that row. That avoids having to convert between characters and doubles, which you're currently (implicitly) doing.

Finally, the addGrade() method ought to take a char and a double (a row and a new grade), rather than a String : you're making a lot of work for yourself with having to process inappropriate data structures.

Once you've done this, calling addGrade for each item should be fairly easy. Once you've extracted a String representing a particular grade (say, String gr = "e77.5" ) then you can add to the list inside your HashMap gradeMap like this:

char row = gr.charAt(0);
double grade = Double.parseDouble(gr.substring(1));
gradeMap.get(row).add(grade);

I think you'll need to supply more info if you need more help than that.

Answer 2

You stated that you need to read from a file, but none of your code is actually reading from a file. This should be your first step. Try looking at BufferedReader documentation as well as numerous posts on this site regarding proper methods to perform file IO operations.

I'm assuming your storing your grades in the 2D gradeTable array like: {Category, grade} . You will need to read each row in your file(BufferedReader has methods for this), parse the string (Look at the String documentation, specifically split or substring/indexOf methods) into category and grade, and then populate your array.

Look into using more dynamic data structures, such as ArrayList . This will allow you to expand the size as you add more grades, as well as not having to copy your array into a new array every time the size expands.