Question

我从下面程序的命令行读取此文件：

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**

GradeBookApp.java

public class GradeBookApp {

public static void main(String[] args) throws IOException {

  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);
}
}

我有另一个包含方法＆＃34; addGrade＆＃34;它接受参数＆＃34; newGradeIn＆＃34;。此参数是正在读取的文件的等级，即a100或e88。对于要添加的每个等级，我将原始2D数组替换为另外一个等级。

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; 
}

我完全不知道如何做到这一点。我知道我应该使用for-each循环，但我不确定如何解决这个问题。

Answer 1

由于您要使用成绩a中的a100来存储100作为学生a的成绩，您应该考虑使用Map而不是2D数组。例如：

Map<String, double[]> gradeTable = new HashMap<>();

public void addGrade(String newGradeIn) {
    String row = newGradeIn.substring(0,1); // use the 'a' as a key in the hashmap to the grades of student `a`
    int grade = Integer.parseInt(newGradeIn.substring(1));
    double[] oldArr = gradeTable.get(row);
    if (oldArr == null) { // when you start - the hash-map is empty so we need to initialize the array
        oldArr = new double[0];
    }
    double[] newArr = Arrays.copyOf(oldArr, oldArr.length + 1);
    newArr[newArr.length - 1] = grade;
    gradeTable.put(row, newArr);
}

用法很简单：

GradeBook g = new GradeBook();
g.addGrade("a100");
g.addGrade("a95");
g.addGrade("b90");
g.addGrade("b95");
System.out.println(Arrays.toString(g.gradeTable.get("a"))); // [100.0, 95.0]
System.out.println(Arrays.toString(g.gradeTable.get("b"))); // [90.0, 95.0]

为文件中的多个值调用方法

1 个答案: