使用日期错误打印每月的日子？

Question

import javax.swing.JOptionPane;

public class Lab42{

    public static void switchExample(){

        String str1;
        int s1, result;

        do {
            str1 = JOptionPane.showInputDialog("Enter the date: ");
            s1 = Integer.parseInt(str1);
            result = s1 % 7;

            switch (result){

                case 1:
                    System.out.printf("• %d falls on a Monday", s1); break;

                case 2:
                    System.out.printf("\n• %d falls on a Tuesday", s1); break;

                case 3:
                    System.out.printf("\n• %d falls on a Wednesday", s1); break;

                case 4:
                    System.out.printf("\n• %d falls on a Thursday", s1); break;

                case 5:
                    System.out.printf("\n• %d falls on a Friday", s1); break;

                case 6:
                    System.out.printf("\n• %d falls on a Saturday", s1); break;

                default:
                    System.out.printf("\n• %d falls on a Sunday", s1); break;

            }
        } while(s1 <= 31 && str1.compareTo("quit") != 0);

    }

    public static void main(String [] args){
        switchExample();
    }
}

output: Exception in thread "main" java.lang.NumberFormatException: For input string: "quit"
    at java.base/java.lang.NumberFormatException.forInputString(NumberFormatException.java:68)
    at java.base/java.lang.Integer.parseInt(Integer.java:658)
    at java.base/java.lang.Integer.parseInt(Integer.java:776)
    at Lab42.switchExample(Lab42.java:12)
    at Lab42.main(Lab42.java:44)

我想在数字1-31之间接受用户的输入，并打印它所在的日子，（假设1号是在星期一），我想让循环继续下去，直到数字大于31或者用户的类型退出。谁能告诉我，我哪里做错了？

谢谢！（我是StackOverflow的新手，如果问题不符合模式请见谅）。

Answer 1

问题是 quit 不能转换为整数，因此，需要先检查输入的值，如果为 quit. 如果输入不是 quit，检查是否可以将其解析成一个 int 并在输入不能解析为整数时进行回环。

具体操作如下。

import javax.swing.JOptionPane;

public class Main {
    public static void main(String[] args) {
        String str1;
        int s1 = 0, result;
        boolean valid;
        do {
            do {
                valid = true;
                str1 = JOptionPane.showInputDialog("Enter the date: ");
                if (str1.equalsIgnoreCase("quit")) {
                    break;
                }
                try {
                    s1 = Integer.parseInt(str1);
                    if (s1 > 31) {
                        break;
                    }

                    result = s1 % 7;

                    switch (result) {
                    case 1:
                        System.out.printf("• %d falls on a Monday", s1);
                        break;

                    case 2:
                        System.out.printf("\n• %d falls on a Tuesday", s1);
                        break;

                    case 3:
                        System.out.printf("\n• %d falls on a Wednesday", s1);
                        break;

                    case 4:
                        System.out.printf("\n• %d falls on a Thursday", s1);
                        break;

                    case 5:
                        System.out.printf("\n• %d falls on a Friday", s1);
                        break;

                    case 6:
                        System.out.printf("\n• %d falls on a Saturday", s1);
                        break;

                    default:
                        System.out.printf("\n• %d falls on a Sunday", s1);
                        break;
                    }

                } catch (NumberFormatException e) {
                    System.out.println("Wrong input. Try again.");
                    valid = false;
                }
            } while (!valid);
        } while (!str1.equalsIgnoreCase("quit"));
    }
}