Question

所以在我的Java课程中，我正在使用eclipse霓虹灯代码来显示根据年份和月份在一个月内的天数。我有所有写的代码，但如果你输入一个数字，然后1-12一个月，我需要一个错误信息弹出，我不知道如何弹出一个输出而不是另一个。以下是我的代码：

import java.util.Scanner; 

public class Month 
{
    public static void main(String[] args)
    {
        // Create a Scanner object to obtain information from user
        Scanner input = new Scanner (System.in);

        int MonthNum; // To hold the month from user input
        int Year; // To hold the year
        int numDays;

        System.out.print("Please enter a month, 1-12:");
        MonthNum = input.nextInt();
        System.out.print("Please enter year:");
        Year = input.nextInt();

        if (MonthNum == 2)
        {
            if( (Year % 4 == 0) && (Year % 400 == 0) && !(Year % 100 == 0) )
                numDays= 29;
            else 
                numDays= 28;
        }
        else if (MonthNum == 1 || MonthNum == 3 || MonthNum == 5 || MonthNum == 7 || MonthNum == 8 || MonthNum == 10 || MonthNum == 12)
            numDays = 31;
        else
            numDays = 30;

        String Monthnam = null;
        if (MonthNum == 1)
            Monthnam = "January";
        else if (MonthNum == 2)
            Monthnam = "Febuary";
        else if (MonthNum == 3)
            Monthnam = "March";
        else if (MonthNum == 4)
            Monthnam = "April";
        else if (MonthNum == 5)
            Monthnam = "May";
        else if (MonthNum == 6)
            Monthnam = "June";
        else if (MonthNum == 7)
            Monthnam = "July";
        else if (MonthNum == 8)
            Monthnam = "August";
        else if (MonthNum == 9)
            Monthnam = "September";
        else if (MonthNum == 10)
            Monthnam = "October";
        else if (MonthNum == 11)
            Monthnam = "November";
        else if (MonthNum == 12)
            Monthnam = "December";

        System.out.print(Monthnam + " " + Year + " " + "has" + " " + numDays + " " + "days");
    }
}

Answer 1

第13行之后你会有一个很大的if / else块

if( MonthNum <1 || MonthNum > 12 ){
    System.out.println("Invalid Month: " + MonthNum)
} 
else {
   ... the rest of your code
}

如果你想提示然后使用while循环

boolean haveInput = false;
while( !haveInput ){
    // get the MonthNum
     if( MonthNum <1 || MonthNum > 12 ){
        System.out.println("Invalid Month: " + MonthNum)
     } 
     else {
        haveInput = true;
     }
 }

 // now the rest of your code

Answer 2

import java.util.Scanner; 

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

    // Create a Scanner object to obtain information from user
    Scanner input = new Scanner (System.in);

    int MonthNum; // To hold the month from user input
    int Year; // To hold the year
    int numDays;

    if( MonthNum < 1 || MonthNum > 12 ){
        System.out.println("Invalid Month: " + MonthNum);
    } 
    else {
    System.out.print("Please enter a month, 1-12:");
    MonthNum = input.nextInt();
    System.out.print("Please enter year:");
    Year = input.nextInt();

    if (MonthNum == 2)
    {
        if( (Year % 4 == 0) && (Year % 400 == 0) && !(Year % 100 == 0) )
            numDays= 29;
            else 
                numDays= 28;
    }
    else if (MonthNum == 1 || MonthNum == 3 || MonthNum == 5 || MonthNum == 7 || MonthNum == 8 || MonthNum == 10 || MonthNum == 12)
        numDays = 31;
    else
        numDays = 30;

    String Monthnam = null;
    if (MonthNum == 1)
        Monthnam = "January";
    else if (MonthNum == 2)
        Monthnam = "Febuary";
    else if (MonthNum == 3)
        Monthnam = "March";
    else if (MonthNum == 4)
        Monthnam = "April";
    else if (MonthNum == 5)
        Monthnam = "May";
    else if (MonthNum == 6)
        Monthnam = "June";
    else if (MonthNum == 7)
        Monthnam = "July";
    else if (MonthNum == 8)
        Monthnam = "August";
    else if (MonthNum == 9)
        Monthnam = "September";
    else if (MonthNum == 10)
        Monthnam = "October";
    else if (MonthNum == 11)
        Monthnam = "November";
    else if (MonthNum == 12)
        Monthnam = "December";

    System.out.print(Monthnam + " " + Year + " " + "has" + " " + numDays + " " + "days");

    }
}}

我如何在java中有两个输出，但只有一个显示取决于结果？

2 个答案: