Question

我正在编写一个程序，每个学生需要用户输入5名学生和4个考试成绩并将其放入数组中。然后它平均学生的分数并给出一个字母等级。该程序还需要输入验证，不接受低于0和超过100的分数。

到目前为止，我的程序验证用户并告诉他们他们输入的数字无效，但我还希望用户在输入无效数字后提示用户重新开始。我已经尝试了几个不同的选项，如下所示（在enterData方法中），但没有一个强制用户重新开始。有什么建议吗？

import java.util.Scanner;

public class GradeBook {
    private String[] names = new String[5];

    private char[] grades = new char[5];

    private double[] scores1 = new double[5];
    private double[] scores2 = new double[5];
    private double[] scores3 = new double[5];
    private double[] scores4 = new double[5];
    private double[] scores5 = new double[5];

    int studentData = 0;
    int studentCount = 0;

    Scanner keyboard = new Scanner(System.in);

    public void enterData() {
        do {
            System.out.println("Enter the student's name:");
            String student = keyboard.nextLine();

            System.out.println("Enter the student's first test score");
            double score1 = Double.parseDouble(keyboard.nextLine());
            if (score1 > 0 || score1 < 100) {
            } else {
                System.out.println("Invalid number");
                continue;
            }


            System.out.println("Enter the student's second test score");
            double score2 = Double.parseDouble(keyboard.nextLine());
            if (score2 > 0 || score2 < 100) {
            } else {
                System.out.println("Invalid number");
                System.out.println("Please start over");
                continue;
            }

            System.out.println("Enter the student's third test score");
            double score3 = Double.parseDouble(keyboard.nextLine());
            if (score3 < 0 || score3 > 100)
                System.out.println("Invalid number");

            System.out.println("Enter the student's fourth test score");
            double score4 = Double.parseDouble(keyboard.nextLine());
            if (score4 < 0 || score4 > 100)
                System.out.println("Invalid number");

            addStudent(student, score1, score2, score3, score4);
            studentData++;
        } while (studentData < 5);
    }


    public String toString() {
        StringBuilder printout = new StringBuilder();
        for (int i = 0; i < names.length; i++) {
            if (names[i] == null)
                continue;
            printout.append("Student name: " + names[i] + "\t" + "Average test score: " +
                    getAverage(i) + "\t" + "Grade: " + grades[i] + "\n");
        }
        return printout.toString();
    }


    private void addStudent(String inName, double scr1, double scr2, double scr3, double scr4) {

        names[studentCount] = inName;
        scores1[studentCount] = scr1;
        scores2[studentCount] = scr2;
        scores3[studentCount] = scr3;
        scores4[studentCount] = scr4;
        grades[studentCount] = getLetterGrade(studentCount);
        studentCount++;
    }


    private double getAverage(int index) {
        double score1 = scores1[index];
        double score2 = scores2[index];
        double score3 = scores3[index];
        double score4 = scores4[index];
        double average = (score1 + score2 + score3 + score4) / 4.0;
        return average;
    }

    private char getLetterGrade(int index) {
        double average = getAverage(index);
        char grade;

        if (average >= 90)
            grade = 'A';
        else if (average >= 80)
            grade = 'B';
        else if (average >= 70)
            grade = 'C';
        else if (average >= 60)
            grade = 'D';
        else
            grade = 'F';


        return grade;
    }

}

我比这更困难。这很好用。

   System.out.println("Enter the student's third test score");
    double score3 = Double.parseDouble(keyboard.nextLine());          
      while (score3 < 0 || score3 > 100)
      {
          System.out.println("Invalid score, plese reenter");
          System.out.println("Enter the student's third test score");
        score3 = Double.parseDouble(keyboard.nextLine());
      }

Answer 1

我知道使用JOptionPanes的方法：

int n = JOptionPane.showConfirmDialog(null,
        "Would you like to start over?",
        "Incorrect Input",
        JOptionPane.YES_NO_OPTION);

if(n == JOptionPane.YES_OPTION)
{
    //start over
}
else
{
    System.exit(0);
}

我猜这与System类中的等价物无关。

Answer 2

您想要做的是流量控制。最简单的方法是：

1）让你的方法返回一个布尔值。如果方法正确退出（输入的所有数据）返回true，如果方法必须退出错误（如本例所示），则返回false（在这种情况下，从{{1}内部返回控制条件。

2）如果方法发现错误，则抛出异常。

在这两种情况下，调用方法的逻辑都必须检查抛出的返回值/异常，如果需要，再次调用该方法。

Answer 3

System.out.println("Enter the student's third test score");
double score3 = Double.parseDouble(keyboard.nextLine());          
  while (score3 < 0 || score3 > 100)
  {
      System.out.println("Invalid score, plese reenter");
      System.out.println("Enter the student's third test score");
    score3 = Double.parseDouble(keyboard.nextLine());
  }

如何在无效输入验证后开始循环？

3 个答案: