爲什麼將本地時間轉換爲GMT時的差異？

Question

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


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

     SimpleDateFormat dateFormatGmt = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"); 

     Calendar presentCal = Calendar.getInstance(TimeZone.getTimeZone("GMT")); 

     System.out.println("With Cal.."+dateFormatGmt.format(presentCal.getTime())); 

     dateFormatGmt.setTimeZone(TimeZone.getTimeZone("GMT")); 

     String currentDateTimeString = dateFormatGmt.format(new Date()); 

     System.out.println("With format.."+currentDateTimeString); 

    } 
} 

OUTPUT：

With Cal..2014-11-14T12:50:23.400Z 
With format..2014-11-14T07:20:23.400Z 

Answer 1

一個日期是在某個時刻，你的TimeZone（S）是兩種格式調用之間的不同。將其更改爲

SimpleDateFormat dateFormatGmt = new SimpleDateFormat(
      "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"); 
    Calendar presentCal = Calendar.getInstance(TimeZone.getTimeZone("GMT")); 
    dateFormatGmt.setTimeZone(TimeZone.getTimeZone("GMT")); // <-- here 
    System.out.println("With Cal.." 
      + dateFormatGmt.format(presentCal.getTime())); // <-- you use it 
                  // here. 
    String currentDateTimeString = dateFormatGmt.format(new Date()); 
    System.out.println("With format.." + currentDateTimeString); 

我在這裏得到正確的輸出。