java - 日期/月份验证

Question

这是我想要做的事情的描述:

First, the program will print "Enter month>," and then the user must enter a number. If the entered number is not in the range of 1 to 12 as the following error message is printed "Improper month.", And the program then ends. If the entered month is correct, the program will print "Enter the day of month>," and then the user must enter a to-speech. If the number does not correspond to a day in the previous input the month, the following error message is printed "Wrong day of the month.", And the program then ends. If both the input month number and the entered day of the month is correct, then the program should print "The correct date.", And then terminated.

但是我在下面收到此错误，但我不明白为什么

Exception in thread "main" java.lang.NumberFormatException: For input string: "java.util.Scanner[delimiters=\p{javaWhitespace}+][position=0][match valid=false][need input=false][source closed=false][skipped=false][group separator=\ ][decimal separator=\,][positive prefix=][negative prefix=\Q-\E][positive suffix=][negative suffix=][NaN string=\Q?\E][infinity string=\Q∞\E]"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
at java.lang.Integer.parseInt(Integer.java:449)
at java.lang.Integer.parseInt(Integer.java:499)
at upp.main(upp.java:10)

import java.util.Scanner;
public class upp {
public static void main(String[] args) {

    int[] numberOfDaysEachMonth = new int[]{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    System.out.println("Enter month > ");
    Scanner month = new Scanner(System.in);
    int userInputMonth = Integer.parseInt(month.toString());
    if (userInputMonth > 0 && userInputMonth < 13) {
        System.out.println("Enter the day of month > ");
        Scanner day = new Scanner(System.in);
        int userInputDay = Integer.parseInt(day.toString());
        if (userInputDay > 0 && userInputDay < numberOfDaysEachMonth[userInputMonth - 1]) {
            System.out.println("Correct date.");
        } else {
            System.out.println("Wrong date.");
        }
    } else {
        System.out.println("Wrong month.");
    }
}
}

Answer 1

 int userInputMonth = Integer.parseInt(month.toString());

它应该是以下语句之一:

// Read as string, convert to int.
int userInputMonth = Integer.parseInt(month.next());

// Read as int using nextInt()
int userInputMonth = month.nextInt();

<小时/>

Scanner day = new Scanner(System.in);

创建 Scanner 的对象后，您无需再次创建它。使用同一对象从 System.in 读取进一步的输入。它应该是以下语句之一。

// Read as string, convert to int.
int userInputDay = Integer.parseInt(month.next());

// Read as int using nextInt()    
int userInputDay = month.nextInt();

<小时/>

您还需要使用<=当天检查的状况而不是 < .

if (userInputDay > 0 && userInputDay <= numberOfDaysEachMonth[userInputMonth - 1])

PS:重命名 Scanner像scanner这样的对象或read然后用它来读取月和日。

<小时/>

import java.util.Scanner;

public class upp {
  public static void main(String[] args) {

    int[] numberOfDaysEachMonth = new int[]{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
    System.out.println("Enter month > ");
    Scanner scanner = new Scanner(System.in);
    int userInputMonth = Integer.parseInt(scanner.next());
    if (userInputMonth > 0 && userInputMonth < 13) {
      System.out.println("Enter the day of month > ");

      int userInputDay = Integer.parseInt(scanner.next());
      if (userInputDay > 0 && userInputDay <= numberOfDaysEachMonth[userInputMonth - 1]) {
        System.out.println("Correct date.");
      } else {
        System.out.println("Wrong date.");
      }
    } else {
      System.out.println("Wrong month.");
    }
  }
}