我必须将用户输入的日期拆分为DDMMYYYY格式.然而，如果你输入70702000，它会显示我的所有3个错误，而不是一个

Question

代码下方：

{
System.out.println("Please enter the date you would like to split");
System.out.println("Please make sure it is in the format DDMMYYYY");
date = sc.nextInt();

day = date / 1000000;
month = (date / 10000) - (day * 100);
year = date - (date / 10000) * (10000);

switch(day) 
{
case 1: case 21: case 31: 
suffix = "st";
break;
case 2: case 22:
suffix = "nd";
break;
case 3: case 23: 
suffix = "rd";
break;
case 4: case 5: case 6: case 7: case 8: case 9: case 10: case 11: case 12: case 13: case 14: case 15: case 16: case 17: case 18: case 19: case 20: case 24: case 25: case 26: case 27: case 28: case 29: case 30:
suffix = "th";
break;

default:
System.out.println("Error, Please enter a valid day (i.e. DD) that is between 01 - 31");
break;
}

switch(month)
{
case 4: case 6: case 9: case 11: 
if ((day < 1) || (day > 30))
{
System.out.println("Error this day does not exist"); 
}
break;
case 1: case 3: case 5: case 7: case 8: case 10: case 12: 
if ((day < 1) || (day > 31))
{
System.out.println("Error this day does not exist");
}
break;
case 2:
if ((day < 1) || (day > 28))
{
if ((day != 29)) 
{
System.out.println("Error this day does not exist");
}
else if ((year % 4 != 0) || ((year % 400 != 0) && (year % 100 == 0)))
{
System.out.println("Error this day does not exist");
}
//If it isn't a leap year, febuary cannot have 29 days
}
break;
default:
System.out.println("Error this day does not exist");
}
switch(month)
{
case 1:
monthName = "January";
break;
case 2:
monthName = "Febuary";
break;
case 3: 
monthName = "March";
break;
case 4:
monthName = "April";
break;
case 5: 
monthName = "May";
break; 
case 6: 
monthName = "June";
break;
case 7:
monthName = "July";
break;
case 8:
monthName = "August";
break;
case 9: 
monthName = "September";
break; 
case 10:
monthName = "October";
break;
case 11: 
monthName = "November";
break;
case 12:
monthName = "December";
default:
System.out.println("Error, Please make sure the month (i.e. MM) is between 01 and 12");
break;
}

if ((day == 29) && (month == 2))
{
System.out.println("It is the 29th day of Febuary in " + year + ".");
}
else 
{
System.out.println("It is the " + day + suffix + " day of " + monthName + " in " + year + ".");
}
}

所以，基本上，当我运行这个程序并输入70702020值时，我会得到以下所有输出：

错误，请输入一个有效日期(即DD(，该日期介于01-31 之间

错误今天不存在

错误，请确保月份(即MM(在01和12 之间

然后它将输出最终输出(只有在用户输入有效日期的情况下才会输出(

Answer 1

break仅中断switch语句

switch语句中的break命令仅跳出switch语句，而不是整个方法。

您有一系列三个switch语句。

• 当您中断第一个switch语句时，控制流会转移到第二个switch声明
• 当您中断第二个switch语句时，控制流将转移到第三个switch声明
• 当您中断第三个switch语句时，控制流将转移到其余语句

编程的核心概念之一是scope。你必须学会从盒子里嵌套的盒子来思考，就像俄罗斯的嵌套玩偶一样。在switch语句中，break命令的作用域只是一个语句，而不是整个方法。switch语句是嵌套在外部方法中的一层作用域。switch语句中的break只能"看到"其直接包含框：switch语句。

java.time

顺便说一句，通过现代java.time类将其解析为文本要简单得多。

try {
LocalDate ld = 
LocalDate
.parse( 
"70702020" , 
DateTimeFormatter.ofPattern( "ddMMuuuu" ) 
)
;
} catch ( DateTimeParseException e ) {
… 
}

无效输入引发DateTimeParseException。

Answer 2

您使用的是开关，而不是if(blah-blah(语句。这意味着，该陈述是真实的，现在会产生错误。您的代码表明您的输入没有任何问题。你的后缀仍然会打印，但打印空引号，因为我相信这是一个空字符串。我建议在使用开关之前先检查一下是否有人进入。或者使用"System.exit(1("，如果输入错误，系统将退出。

编辑：同样，根据计算，你的一天将等于"70"，从而产生其他错误。

Answer 3

我建议查看注释，然后自己执行代码。我补充一些意见。

public class TestFormatDate{
public static void main(String []args){
System.out.println("Please enter the date you would like to split");
System.out.println("Please make sure it is in the format DDMMYYYY");
//your input:70702020
int date = 70702020;
//70
int day = date / 1000000;
//70
int month = (date / 10000) - (day * 100);
//2020
int year = date - (date / 10000) * (10000);
String suffix = null;
String monthName = null;
switch(day) 
{
case 1: case 21: case 31: 
suffix = "st";
break;
case 2: case 22:
suffix = "nd";
break;
case 3: case 23: 
suffix = "rd";
break;
case 4: case 5: case 6: case 7: case 8: case 9: case 10: case 11: case 12: case 13: case 14: case 15: case 16: case 17: case 18: case 19: case 20: case 24: case 25: case 26: case 27: case 28: case 29: case 30:
suffix = "th";
break;
// day is 70, so the default is executed.
default:
System.out.println("Error, Please enter a valid day (i.e. DD) that is between 01 - 31");
break;
}
switch(month)
{
case 4: case 6: case 9: case 11: 
if ((day < 1) || (day > 30))
{
System.out.println("Error this day does not exist"); 
}
break;
case 1: case 3: case 5: case 7: case 8: case 10: case 12: 
if ((day < 1) || (day > 31))
{
System.out.println("Error this day does not exist");
}
break;
case 2:
if ((day < 1) || (day > 28))
{
if ((day != 29)) 
{
System.out.println("Error this day does not exist");
}
else if ((year % 4 != 0) || ((year % 400 != 0) && (year % 100 == 0)))
{
System.out.println("Error this day does not exist");
}
//If it isn't a leap year, febuary cannot have 29 days
}
break;
// month is 70, so the default is executed.
default:
System.out.println("Error this day does not exist");
}
switch(month)
{
case 1:
monthName = "January";
break;
case 2:
monthName = "Febuary";
break;
case 3: 
monthName = "March";
break;
case 4:
monthName = "April";
break;
case 5: 
monthName = "May";
break; 
case 6: 
monthName = "June";
break;
case 7:
monthName = "July";
break;
case 8:
monthName = "August";
break;
case 9: 
monthName = "September";
break; 
case 10:
monthName = "October";
break;
case 11: 
monthName = "November";
break;
case 12:
monthName = "December";
// month is 70, so the default is executed.
default:
System.out.println("Error, Please make sure the month (i.e. MM) is between 01 and 12");
break;
}
if ((day == 29) && (month == 2))
{
System.out.println("It is the 29th day of Febuary in " + year + ".");
}
// day is 70, so the else is executed.
else 
{
System.out.println("It is the " + day + suffix + " day of " + monthName + " in " + year + ".");
}
}
}