创建构造方法

Question

有一个班级计划，我正在与多个班级一起工作。在 classroll 类中，我有一个构造方法“ClassRoll (String f) {”，假设 ....

从输入文件 f 中读取班级卷数据，为每个学生创建学生对象并将它们添加到学生的 ArrayList 中。 输入文件的第一行包含课程标题。每个学生的数据显示在一个单独的行中，由名字、姓氏、score1、score 2 和 score3 组成，至少用一个空格分隔。

下面我将展示 classroll 类和我尝试调用该构造函数的主要方法。每次我运行程序时，我都会收到来自该构造函数的错误。我需要有关如何正确创建该构造函数来完成它需要做的事情的帮助，因为我的尝试不起作用。任何帮助都将不胜感激，谢谢。

public class ClassRoll {

private ArrayList<Student> students = new ArrayList<Student>();
private String title;
private String filename = "data.txt";


 ClassRoll(String f) {      
    Scanner kb = new Scanner(System.in);
    String inpFileName = kb.next();
    File inpFile = new File(inpFileName);

    boolean firstline = true;
    while(kb.hasNextLine()){
        if(firstline){
            title = kb.nextLine();
            firstline = false;
        }
        else{
            String fName = kb.nextLine();
            String lName = kb.nextLine();
            int score1 = kb.nextInt();
            int score2 = kb.nextInt();
            int score3 = kb.nextInt();

            students.add(new Student(fName, lName));

        }
    }


}


void Remove() {
    Scanner kb = new Scanner(System.in);

    System.out.println("What is the Student's first name?");
    String fName = kb.next();

    System.out.println("What is the Student's last name?");
    String lName = kb.next();

    Student s = new Student(fName, lName);

    for (int i = 0; i < students.size(); i++) {
        if (s.compareTo(students.get(i)) == 0) {
            students.remove(i);

        } else {
            System.out.println("Error: Student is not in Class");
        }

    }

}

void Display() {
    DecimalFormat fmt = new DecimalFormat("0.00");
    System.out.println("\t\t\t" + title);

    double classAverage = 0.0;

    for (int i = 0; i < students.size(); i++) {
      Student s = (Student) students.get(i);
      System.out.print(s.toString());
      System.out.println("\t" + fmt.format(s.getAverage()));
      classAverage = classAverage + s.getAverage();
    }
    System.out.println("\t\t\t" + fmt.format(classAverage /      
       students.size()));


}

void Add() {
    Scanner kb = new Scanner(System.in);

    System.out.println("What is the Student's first name?");
    String fName = kb.next();

    System.out.println("What is the Student's last name?");
    String lName = kb.next();

    System.out.println("What is the Student's first score?");
    int score1 = kb.nextInt();

    System.out.println("What is the Student's second score?");
    int score2 = kb.nextInt();

    System.out.println("What is the Student's third score?");
    int score3 = kb.nextInt();

    Student s = new Student(fName, lName);

    for (int i = 0; i < students.size(); i++) {
        if (s.compareTo(students.get(i)) == 0) {
            System.out.println("Student already in class");
        } else {
            students.add(s);
        }
    }
}

void changeScore1() {
    Scanner kb = new Scanner(System.in);

    System.out.println("What is the Student's first name?");
    String fName = kb.next();

    System.out.println("What is the Student's last name?");
    String lName = kb.next();

    System.out.println("What is the Student's first score?");
    int score1 = kb.nextInt();

    Student s = new Student(fName, lName);

    for (int i = 0; i < students.size(); i++) {
        if (s.compareTo(students.get(i)) == 0) {
            s.setScore1(i);
        } else {
            System.out.println("Error: Student is not in Class");
        }

    }

}

void changeScore2() {
    Scanner kb = new Scanner(System.in);

    System.out.println("What is the Student's first name?");
    String fName = kb.next();

    System.out.println("What is the Student's last name?");
    String lName = kb.next();

    System.out.println("What is the Student's first score?");
    int score1 = kb.nextInt();

    Student s = new Student(fName, lName);

    for (int i = 0; i < students.size(); i++) {
        if (s.compareTo(students.get(i)) == 0) {
            s.setScore2(i);
        } else {
            System.out.println("Error: Student is not in Class");
        }

    }

}

void changeScore3() {
    Scanner kb = new Scanner(System.in);

    System.out.println("What is the Student's first name?");
    String fName = kb.next();

    System.out.println("What is the Student's last name?");
    String lName = kb.next();

    System.out.println("What is the Student's first score?");
    int score1 = kb.nextInt();

    Student s = new Student(fName, lName);

    for (int i = 0; i < students.size(); i++) {
        if (s.compareTo(students.get(i)) == 0) {
            s.setScore3(i);
        } else {
            System.out.println("Error: Student is not in Class");
        }

    }

}

public void find() {
    Scanner kb = new Scanner(System.in);

    System.out.println("What is the Student's first name?");
    String fName = kb.next();

    System.out.println("What is the Student's last name?");
    String lName = kb.next();

     Student s = new Student(fName, lName);

    for (int i = 0; i < students.size(); i++) {
        if (s.compareTo(students.get(i)) == 0){
            System.out.println(s);
        }
    }
}

public void sortAverage() {
    for (int i = 0; i < students.size() - 1; i++) {
        for (int j = i + 1; j < students.size(); j++) {
            Student s1 = (Student) students.get(i);
            Student s2 = (Student) students.get(j);
            if (s1.getAverage() < s2.getAverage()) {
                students.set(i, s2);
                students.set(j, s1);
            }
        }
    }
}

public void sortNames() {
    for (int i = 0; i < students.size() - 1; i++) {
        for (int j = i + 1; j < students.size(); j++) {
            Student s1 = (Student) students.get(i);
            Student s2 = (Student) students.get(j);
            if (s1.compareTo(s2) > 0) {
                students.set(i, s2);
                students.set(j, s1);
            }
        }
    }
}

public void save() throws IOException {
PrintWriter out = new PrintWriter(filename);
out.println(title);
for (int i = 0; i < students.size(); i++) {
    Student s = (Student) students.get(i);
    out.println(s.toString());
}
out.close();

 }}

主要方法

public class Assignment4 {

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

    Scanner input = new Scanner(System.in);
    System.out.print("Enter the name of the input file ->");
    String fileName = input.next();

    ClassRoll c = new ClassRoll(fileName);


    prompt();
    System.out.print("Enter a command --> ");
    String ans = input.next();

    while (!(ans.equalsIgnoreCase("q") || ans.equalsIgnoreCase("quit"))) {
        if (!(ans.equalsIgnoreCase("a") || ans.equalsIgnoreCase("Add")
                || ans.equalsIgnoreCase("s")|| ans.equalsIgnoreCase("average")
                || ans.equalsIgnoreCase("n")|| ans.equalsIgnoreCase("names")
                || ans.equalsIgnoreCase("r") || ans.equalsIgnoreCase("remove")
                || ans.equalsIgnoreCase("f") || ans.equalsIgnoreCase("find")
                || ans.equalsIgnoreCase("d") || ans.equalsIgnoreCase("display"))) {
            System.out.println("Bad Command");
        } else {
            switch (ans.charAt(0)) {
                case 'a':
                    c.Add();
                    break;
                case 's':
                    c.sortAverage();
                    c.Display();
                    break;
                case 'n':
                    c.sortNames();
                    c.Display();
                    break;
                case 'r':
                    c.Remove();
                    c.Display();
                    break;
                case 'f':
                    Student s = c.find();
                    if (s == null) {
                        System.out.println("Student not found");
                    } else {
                        System.out.println(s.toString());
                    }
                    break;
                case 'd':
                    c.Display();

                    break;
            }
        }
        prompt();
        System.out.print("Enter a command --> ");
        ans = input.next();
    }
    c.save();
    System.out.println("Thank you for using this program");

}

public static void prompt() {
    System.out.println("Enter one of the following commands");

    System.out.println("a or Add to add a student in the classroll");

    System.out.println("sa or average to sort the students based on their average");

    System.out.println("sn or names to sort the students based on their last names");

    System.out.println("r or remove to remove a student from the class roll");

    System.out.println("f or find to find a student in the class roll");

    System.out.println("d or display to display the class roll");

    System.out.println("q or quit to exit the program");
}

}

学生班

public class Student {

private String fName;

private String lName;

private Exams scores;

Student(String fn, String ln) {
    fName = fn;
    lName = ln;
    scores = new Exams();

}

public void setScore1(int sc) {
    int score1 = 0;
    score1 = sc;

}

public void setScore2(int sc) {
    int score2 = 0;
    score2 = sc;

}

public void setScore3(int sc) {
    int score3 = 0;
    score3 = sc;

}

public String toSring() {
    return String.format("%-10s %-10s %4.2f\n", fName, lName, scores);
}

public double getAverage() {
    return (scores.getScore1() + scores.getScore2()
            + scores.getScore3()) / 3.0;
}

public int compareTo(Student s) {
    String name1 = lName + "  " + fName;
    String name2 = s.lName + "  " + s.fName;

    if((lName + "  " + fName).compareTo(s.lName + "  " + s.fName)> 0)
        return 1;
    else if ((lName + "  " + fName).compareTo(s.lName + "  " + s.fName)< 0)
        return -1;
    else return 0;
}
}

Answer 1

这个异常是由 Scanner 抛出的

由 Scanner 抛出以指示检索到的令牌不 匹配预期类型的​​模式，或者令牌不在 预期类型的​​范围。

请检查您的输入文件。它会解决你的问题。

您的数据必须是行分隔的。

代码sn-ps

Scanner kb = new Scanner(new FileInputStream(new File("d://app//test.txt")));
boolean firstline = true;
        while(kb.hasNext()) {
            if (firstline) {
                title = kb.nextLine();
                firstline = false;
            } else {
                String fName =kb.next() ;
                String lName = kb.next();
                int score1 = kb.nextInt();
                int score2 = kb.nextInt();
                int score3 = kb.nextInt();

                students.add(new Student(fName, lName));
            }
        }