java 使用 Joda 时间减去 1 小时到 DateTime
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/17000375/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
minus 1 hour to DateTime using Joda Time
提问by Maguzu
I just want to subtract 1 hour from a DateTimeI tried looking it up on Google and I found that there is a method called minus that takes a copy of the date and take a specific duration right here: http://www.joda.org/joda-time/apidocs/org/joda/time/DateTime.html#minus(long)
我只是想从DateTime我尝试在 Google 上查找它时减去 1 小时，我发现有一种方法叫做减号，它获取日期的副本并在此处获取特定的持续时间：http: //www.joda.org /joda-time/apidocs/org/joda/time/DateTime.html#minus(long)
But I don't know how to use it and I can't an find a example on the internet.
但我不知道如何使用它，我在互联网上找不到一个例子。
Here's my code:
这是我的代码：
String string1 = (String) table_4.getValueAt(0, 1);
String string2= (String) table_4.getValueAt(0, 2);
DateTimeFormatter dtf = DateTimeFormat.forPattern("hh:mm a").withLocale(Locale.ENGLISH);
DateTime dateTime1 = dtf.parseDateTime(string1.toString());
DateTime dateTime2 = dtf.parseDateTime(string2.toString());
final String oldf = ("hh:mm a");
final String newf= ("hh.mm 0");
final String newf2= ("hh.mm a");
final String elapsedformat = ("hh.mm");
SimpleDateFormat format2 = new SimpleDateFormat(oldf);
SimpleDateFormat format2E = new SimpleDateFormat(newf);
Period timePeriod = new Period(dateTime1, dateTime2);
PeriodFormatter formatter = new PeriodFormatterBuilder()
.appendHours().appendSuffix(".")
.appendMinutes().appendSuffix("")
.toFormatter();
String elapsed = formatter.print(timePeriod);
table_4.setValueAt(elapsed,0,3);
DecimalFormat df = new DecimalFormat("00.00");
System.out.println(dateTime1);
table_4.setValueAt("", 0, 4);
table_4.setValueAt("", 0, 5);
Sample Data:
样本数据：
dateTime1: 08:00 AM
dateTime2: 05:00 PM
the period will be 9 hours. but i want it to be 8 hrs only because i want to subtract the lunch break in my program.
时间为9小时。但我希望它是 8 小时，因为我想在我的程序中减去午休时间。
i tried it with this stupid code:
我用这个愚蠢的代码试过了：
dateTime1.minus(-1)
I also tried parsing string1to double so I can subtract it by one.
我还尝试将其解析string1为加倍，这样我就可以将其减一。
double strindtoD = Integer.parseInt(string1);
I also tried making another DateTimeand use period to get the difference of the two time
我也尝试制作另一个DateTime并使用期间来获得两次时间的差异
String stringOneHour = ("01:00 AM");
DateTime dateTime3 = dtf.parseDateTime(stringOneHour.toString());
Period timePeriod = new Period(dateTime3, dateTime1);
回答by fge
Just use:
只需使用：
dateTime.minusHours(1)
This is documented in the API.
Note that DateTimeobjects are immutable, so the operation alone has no effect. You need to assign the result of this method to a new object (or replace itself):
请注意，DateTime对象是不可变的，因此单独的操作没有任何效果。您需要将此方法的结果分配给新对象（或替换自身）：
dateTime = dateTime.minusHours(1);
As to how to obtain a Periodout of the difference between two DateTimes, you must first go through an Interval:
至于如何Period从两个DateTimes之间的差异中获得一个，首先要经过一个Interval：
Period period = new Interval(begin, end).toPeriod();
Linkto a SO post explaining why there is both Periodand Interval.
链接到解释为什么同时存在Period和的 SO 帖子Interval。
Side note: Joda Time uses a LOT of indirections in its API; as such reading the Javadoc not only requires one to read the methods for one class, but also look at the list of inherited methods from all the inherited abstract classes/interfaces; for instance, a DateTimeis also a ReadableInstant. One you get used to it, though, it's a breeze.
旁注：Joda Time 在其 API 中使用了大量间接引用；因此，阅读 Javadoc 不仅需要阅读一个类的方法，还需要查看所有继承的抽象类/接口的继承方法列表；例如， aDateTime也是 a ReadableInstant。一个你习惯了，不过，这是一件轻而易举的事。
回答by Lance Reid
If you are using an older version of org.joda.time.DateTime then you can use minus(ReadablePeriod period) method like this
如果您使用的是 org.joda.time.DateTime 的旧版本，那么您可以使用这样的 minus(ReadablePeriod period) 方法
Date date = LocalDate.now().minus(new Period(1, 0, 0, 0)).toDate();
where Period accepts int hours, int minutes, int seconds, int millis parameters
其中 Period 接受整数小时、整数分钟、整数秒、整数毫秒参数
