如何从设置日期数据类型中的引用更改日期格式

Question

I am getting date in an date object

Date s = ((java.util.Date) ((Object[]) object)[++i]);

i need to set this format 20130509 06:00

so for this I have choosen ..

SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd HH:mm");
    String s1 = sdf.format(s);

now again my task is to put back in date object that string s1, please advise how to achieve this

Answer 1

Date doesn't have a textual format - or even a time zone or calendar. It's just a number of milliseconds since the unix epoch. There's nothing to set within Date .

You need to differentiate between your fundamental data, and a textual representation of that data - in the same way as the int value 16 is the same as 0x10. I can't think of any time where I've found it appropriate to carry a textual representation of a date around with the date itself. In various places in your program you may well find that you need different representations for the same date - but it's usually the same representation for all dates at that specific part of the program.

As an aside, you should consider using Joda Time instead of java.util.Date - it provides you with a much richer set of types to consider, so you can express what your program is actually dealing with (just a date, just a time, a date/time in a particular time zone etc).

Answer 2

Ideally, you shouldn't try to translate to String format and back again. You should persist the original value and just use the String format for display purpose only.

Otherwise, you can use SimpleDateFormat.parse method.

Answer 3

I recommend using Joda time... how given what you've got you can just do

sdf.parse

@Test
public void testDateStringConversion() throws ParseException {
    Date date  = new Date();
    SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd HH:mm");
    String s1 = sdf.format(date);

    Date date2 = sdf.parse(s1);               // seconds won't match
    String s2 = sdf.format(date2);
    assertEquals(s1, s2);
}