Java:根据时区计算月末日期

问题描述

我有方法根据时区查找月末日期.

I have method to find month end date based on the timezone.

Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("CET"));
calendar.set(
    Calendar.DAY_OF_MONTH, 
    calendar.getActualMaximum(Calendar.DAY_OF_MONTH)
);
System.out.println(calendar.getTime());`

它显示输出:Thu Aug 30 18:04:54 PDT 2018.

但是，它应该给我 CET 的输出.

It should, however, give me an output in CET.

我错过了什么?

推荐答案

Calendar.getTime() 方法返回一个 Date 对象，然后将其打印在代码中.问题是 Date 类 不包含任何时区的概念，即使您使用 Calendar.getInstance() 指定了时区称呼.是的，这确实令人困惑.

The Calendar.getTime() method returns a Date object, which you then printed in your code. The problem is that the Date class does not contain any notion of a timezone even though you had specified a timezone with the Calendar.getInstance() call. Yes, that is indeed confusing.

因此，为了在特定时区打印 Date 对象，您必须使用 SimpleDateFormat 类，打印前必须调用 SimpleDateFormat.setTimeZone() 指定时区.

Thus, in order to print a Date object in a specific timezone, you have to use the SimpleDateFormat class, where you must call SimpleDateFormat.setTimeZone() to specify the timezone before you print.

这是一个例子:

import java.util.Calendar;
import java.util.TimeZone;
import java.text.SimpleDateFormat;

public class TimeZoneTest {

    public static void main(String argv[]){
        Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("CET"));
        calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
        System.out.println("calendar.getTime(): " + calendar.getTime());

        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MMM-dd HH:mm:ss z");
        sdf.setTimeZone(TimeZone.getTimeZone("CET"));
        System.out.println("sdf.format(): " + sdf.format(calendar.getTime()));
     }
}

这是我电脑上的输出:

calendar.getTime(): Fri Aug 31 01:40:17 UTC 2018
sdf.format(): 2018-Aug-31 03:40:17 CEST

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