Date comparision in java

[Tusshar Fasate]

Hi ,
I want to compare two dates.
Out of two dates ,I know the fomat of one date
but I dont know the format of second date.
So how can I do comparision between these two dates.
Thanks.

[Jesper de Jong]

So, you have those dates as strings? First, you'll have to convert them to java.util.Date objects. You can do that using java.text.SimpleDateFormat (read the API documentation for that class).

But if you don't know what the format of the second date is, it is going to be very hard. The computer can't magically figure that out for you... Note that dates can be written in ambiguous ways: for example, does "01/03/10" mean 1 March 2010, 3 January 2010 or maybe even 10 March 2001?

Once you have the dates as Date objects, you can use methods such as after() and before() on the Date objects (again, lookup the API documentation) to compare them.

[Tusshar Fasate]

Thanks for reply.
But this is the case i want.
Is there any other suggestions...?

[Rob Spoor]

The main question is, why don't you know the second format? Where is this date coming from? If it is from user input, simply limit the user to a format you know. You can even allow a select group of formats. For instance:

public Date getDate(String s, String... patterns) throws ParseException
{
    for (String pattern: patterns)
    {
        DateFormat format = new SimpleDateFormat(pattern);
        ParsePosition position = new ParsePosition(0);
        Date date = format.parse(s, position); // returns null if invalid
        if (date != null)
        {
            return date;
        }
    }
    // not valid for any of the patterns
    throw new ParseException("Invalid date", 0);
}

[Jesper de Jong]

tushartrue fasate wrote:Thanks for reply.
But this is the case i want.
Is there any other suggestions...?

First you have to answer the following question for yourself: What are you going to do if you get for example "01/03/10" for the second date? You'll have to decide for yourself how that should be handled; we can't tell you, because we don't know the requirements for the program you're writing. Without an answer to that question, it makes no sense to ask for Java code.

[Jiten Kothari]

  public static int diffDays(Date start, Date end) {
    
        Calendar startCalIn = Calendar.getInstance();
        startCalIn.clear();
        startCalIn.setTime(start);

        Calendar endCalIn = Calendar.getInstance();
        endCalIn.clear();
        endCalIn.setTime(end);

        Calendar startDate = Calendar.getInstance();
        startDate.clear();
        Calendar endDate = Calendar.getInstance();
        endDate.clear();

        startDate.set(startCalIn.get(Calendar.YEAR), startCalIn.get(Calendar.MONTH), startCalIn.get(Calendar.DATE), 0, 0, 0);
        endDate.set(endCalIn.get(Calendar.YEAR), endCalIn.get(Calendar.MONTH), endCalIn.get(Calendar.DATE), 0, 0, 0);

        BigDecimal begDec = new BigDecimal("" + startDate.getTimeInMillis());
        BigDecimal endDec = new BigDecimal("" + endDate.getTimeInMillis());
        BigDecimal diff = endDec.subtract(begDec);
        BigDecimal day = new BigDecimal("" + 86400000);
        BigDecimal result = diff.divide(day, 0, BigDecimal.ROUND_HALF_UP);

        return result.intValue();
    }  

cheers

[Henry Wong]

This is a past similar topic, if you are interested...

https://coderanch.com/t/482942/java/java/parse-user-entered-Date-Date

Henry