在我提出一个关于减去时间的问题之前，我认为我已经拥有了它。但是当我调试时，出现了几个错误。基本上我要问的是创建一个打卡时钟，但我不能使用Java Calendar API。
用户将输入开始时间和他们打孔的时间，并计算时间之间的差异。
我的工作效果不好，我不知道为什么。例如，如果上午4:00是开始，上午12:00是结束，则返回8小时00分钟。那是不对的。我以为我为可能性创建了一个if语句。
这是我的代码：
public static void elapsedTime()
{
Scanner reader = new Scanner (System.in);
System.out.print("Enter the beginning hour: ");
int startingHour = reader.nextInt();
System.out.print("Enter the beginning minute(s): ");
int startingMin = reader.nextInt();
System.out.print("Enter AM/PM: ");
reader.nextLine();
String startingTOD = reader.nextLine();
System.out.print("Enter the ending hour: ");
int endingHour = reader.nextInt();
System.out.print("Enter the ending minute(s): ");
int endingMin = reader.nextInt();
System.out.print("Enter AM/PM: ");
reader.nextLine();
String endingTOD = reader.nextLine();
System.out.println();
int hours;
int minutes = endingMin - startingMin;
String Am = "am" ;
String Pm = "pm" ;
if (endingTOD.equalsIgnoreCase(startingTOD) && minutes < 0 )
{
hours = (endingHour - startingHour) -1 ;
minutes = minutes + 60 ;
System.out.println(hours + " " + minutes);
}
else if (endingHour > startingHour&& endingTOD.equalsIgnoreCase(startingTOD) & minutes > 0 )
{
hours = endingHour - startingHour;
System.out.println(hours + " " + minutes);
}
else if (endingHour > startingHour && endingTOD.equalsIgnoreCase(startingTOD) && minutes == 0 )
{
hours = (endingHour-startingHour);
minutes = 0;
System.out.println(hours + " " + minutes);
}
else if (endingHour < startingHour && endingTOD.equalsIgnoreCase(startingTOD) && minutes == 0 )
{
hours = (endingHour-startingHour) + 12;
minutes = 0;
System.out.println(hours + " " + minutes);
}
else if ( endingHour==startingHour && minutes == 0)
{
hours = 12;
minutes = 0;
System.out.println(hours + " " + minutes);
}
else if (( endingTOD.equalsIgnoreCase(Pm) && startingTOD.equalsIgnoreCase(Am)) && minutes > 0)
{
hours = (endingHour - startingHour) + 12;
System.out.println(hours + " " + minutes);
}
else if (( endingTOD.equalsIgnoreCase(Pm) && startingTOD.equalsIgnoreCase(Am)) && minutes < 0)
{
hours = (endingHour - startingHour) -1 ;
minutes = minutes + 60 ;
System.out.println(hours + " " + minutes);
}
else if (endingHour > startingHour && ( endingTOD.equalsIgnoreCase(Pm) && startingTOD.equalsIgnoreCase(Am)) && minutes == 0)
{
hours = (endingHour-startingHour) + 12;
minutes = 0;
System.out.println(hours + " " + minutes);
}
else if (endingHour < startingHour &&( endingTOD.equalsIgnoreCase(Pm) && startingTOD.equalsIgnoreCase(Am)) && minutes == 0)
{
hours = (endingHour - startingHour) +24;
minutes = 0;
System.out.println(hours + " " + minutes);
}
else if (endingHour < startingHour &&( endingTOD.equalsIgnoreCase(Pm) && startingTOD.equalsIgnoreCase(Am)) && minutes > 0)
{
hours = (endingHour - startingHour) + 2;
System.out.println(hours + " " + minutes);
}
}
答案 0 :(得分：1)
鉴于您无法使用Java Calendar API，您的方法虽然不是非常模块化，但乍一看看起来很合理。魔鬼在细节中。
日期时间计算的技巧是所有角落情况。这就是为什么没有人想编写和维护这样的东西，甚至Sun / Oracle一次又一次地弄错了。
证明您的代码适用于所有条件都很困难。您最好减少范围并降低要求。 12或24小时钟？如果24小时，我们从0h或1h开始吗？我们是否跨越了几天？我们预计会过夜吗？等
但你的任务是以模12或24的方式比较小时数（除非你的要求说你不需要＆＃34;翻转＆＃34;或跨越12或24小时的界限。）真正的诀窍是将小时视为一系列栅栏柱和轨道，并计算轨道。一次性错误将成为你在这里存在的祸根。
我的建议是至少使用Java Calendar API来仔细检查结果。
答案 1 :(得分：0)
不是试图重新发明轮子并自己实现日期减法逻辑，而是尝试覆盖所有角落情况，您可以利用内置的Java Date Arithmetic。
像这样（将此代码复制到TimeDifference.java并运行）：
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Scanner;
import java.util.Calendar;
import java.util.SimpleTimeZone;
import java.util.TimeZone;
import java.util.concurrent.TimeUnit;
public class TimeDifference {
public static void elapsedTime() {
Scanner reader = new Scanner(System.in);
System.out.print("Enter the beginning hour: ");
int startingHour = reader.nextInt();
System.out.print("Enter the beginning minute(s): ");
int startingMin = reader.nextInt();
System.out.print("Enter AM/PM: ");
reader.nextLine();
String startingTOD = reader.nextLine();
String[] ids = TimeZone.getAvailableIDs(-8 * 60 * 60 * 1000);
// if no ids were returned, something is wrong. get out.
if (ids.length == 0)
System.exit(0);
// create a Pacific Standard Time time zone
SimpleTimeZone pdt = new SimpleTimeZone(-8 * 60 * 60 * 1000, ids[0]);
// set up rules for daylight savings time
pdt.setStartRule(Calendar.APRIL, 1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);
pdt.setEndRule(Calendar.OCTOBER, -1, Calendar.SUNDAY,
2 * 60 * 60 * 1000);
// create a GregorianCalendar with the Pacific Daylight time zone
// and the current date and time
Calendar startingCalendar = new GregorianCalendar(pdt);
Calendar endingCalendar = new GregorianCalendar(pdt);
Date trialTime = new Date();
startingCalendar.setTime(trialTime);
endingCalendar.setTime(trialTime);
startingCalendar.set(java.util.Calendar.HOUR, startingHour);
startingCalendar.set(java.util.Calendar.MINUTE, startingMin);
if (startingTOD.equalsIgnoreCase("AM")) {
startingCalendar.set(java.util.Calendar.AM_PM, 0);
} else if (startingTOD.equalsIgnoreCase("PM")) {
startingCalendar.set(java.util.Calendar.AM_PM, 1);
} else {
System.out.println("invalid starting AM/PM. exiting..");
System.exit(-1);
}
System.out.print("Enter the ending hour: ");
int endingHour = reader.nextInt();
System.out.print("Enter the ending minute(s): ");
int endingMin = reader.nextInt();
System.out.print("Enter AM/PM: ");
reader.nextLine();
String endingTOD = reader.nextLine();
System.out.println();
// get the supported ids for GMT-08:00 (Pacific Standard Time)
endingCalendar.set(java.util.Calendar.HOUR, endingHour);
endingCalendar.set(java.util.Calendar.MINUTE, endingMin);
if (endingTOD.equalsIgnoreCase("AM")) {
endingCalendar.set(java.util.Calendar.AM_PM, 0);
} else if (endingTOD.equalsIgnoreCase("PM")) {
endingCalendar.set(java.util.Calendar.AM_PM, 1);
} else {
System.out.println("invalid ending AM/PM. exiting..");
/* Exit program */
System.exit(-1);
}
long startingTimeMillis = startingCalendar.getTimeInMillis();
long endingTimeMillis = endingCalendar.getTimeInMillis();
long timeDifferenceMillis = endingTimeMillis - startingTimeMillis;
System.out.println(String.format("Time difference between starting and ending time (in minutes and hours): %d hours, %d minutes",
TimeUnit.MILLISECONDS.toHours(timeDifferenceMillis),
TimeUnit.MILLISECONDS.toMinutes(timeDifferenceMillis) -
TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(timeDifferenceMillis))
));
reader.close();
}
public static void main(String[] args) {
elapsedTime();
}
}