Comparing only dates and not timestamp

[Abdul Mohsin]

Hi,

I want to compare two dates neglecting there timestamp, means if two dates point to same 11th Feb then they should be equals (date1.after(date2) and date1.before(date2) both should be false).


I want the better way of doing it , currently I am doing it as setting hour,minute,second,millisecond as 0 and AM to both of the times and then comparing it.

Please suggest if there is a better way of doing it.

[Campbell Ritchie]

Have you tried a Comparator? You can pass the day month year part and compare them alone.
It is quite permissible for a Comparator to return 0 when the equals() method returns false.

[Bill Shirley]

if (a.getDate() == b.getDate() && 
a.getMonth() == b.getMonth() &&
a.getYear() == b.getYear())
sameDate = true;

That should work.
Put it in its own method if you want it to be cleaner.

Those methods are marked as deprecated in Java 5.0 - not sure what th suggested new way should be. I think it involves Calendar.


(aside: English note - "I want to compare two dates neglecting their timestamps", I'm not trying to be rude, there's a lot of English as a second language on The Ranch, and a lot of "what should I learn for a job interview", and better written and oral communications are at least as high as programming skills!, and their/there/they're is a common English problem, and a nitpick of many people (including me )

[Abdul Mohsin]

Hi Bill,

Sorry for grammatical mistakes, your code is only checking for the equivalence of two dates and not doing any comparison, I need to compare and then perform some operation.

Currently I am implementing the logic as:

public static void main(String[] args) throws Exception{
String startDate="14-FEB-08";

SimpleDateFormat sdf = new java.text.SimpleDateFormat( "dd-MMM-yy" );


Calendar cal =Calendar.getInstance();
cal.set(Calendar.MINUTE, 0);
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.set(Calendar.SECOND, 0);
cal.set(Calendar.MILLISECOND, 0);


System.out.println(" cal :"+cal.getTime());
 
Calendar calOfStartDate=Calendar.getInstance();



Date startDate1=(Date) sdf.parse(startDate );

System.out.println("********:"+startDate1.getTime());
calOfStartDate.setTime(startDate1);

System.out.println(" calOfString:"+calOfStartDate.getTime());
System.out.println("Current date :"+cal.getTimeInMillis()+" start date:"+calOfStartDate.getTimeInMillis());
if(calOfStartDate.after(cal)){
System.out.println("start date is after current date");

}
else if(cal.after(calOfStartDate)){
System.out.println("start date is before current date");
}
else if(calOfStartDate.equals(cal)){
System.out.println("both are equal");
}




}    

but I am not happy with this current implementation and want to improve it further.

Please suggest.

[Joanne Neal]

Have you tried dividing the value returned by getTimeInMillis by the number of milliseconds in a day ? Try it for various Calendar objects that represent different times on the same day. Compare the results and see if you can see a way to make use of them.

[Abdul Mohsin]

Hi Joanne,

Can you please explain your approach further with code,
I tried your approach

 long dateDiff=(cal.getTimeInMillis()/ 24*60*60*1000 -calOfStartDate.getTimeInMillis()/ 24*60*60*1000) ;   

// output 12960000000000 , refer the code posted earlier
but it didn't worked.

[Joanne Neal]

Try

long sid = 24 * 60 * 60 * 1000;
long dateDiff=((cal.getTimeInMillis() / sid) - (calOfStartDate.getTimeInMillis() / sid));
System.out.println(dateDiff);

[Bill Shirley]

Abdul,
Your order of operations got you in trouble.

a / b * c == (a / b) * c

you wanted

a / (b * c)

import java.util.Calendar;
import java.util.Comparator;
 
public class MyComparator
implements Comparator<Calendar>{

public int compare(Calendar a, Calendar b) {
long aValue = a.getTimeInMillis() / (1000 * 60 * 60 * 24);
long bValue = b.getTimeInMillis() / (1000 * 60 * 60 * 24);
int diff = (int) (aValue - bValue);
return diff;
}

public boolean equals(Object anotherComparator) {
// should implement more complexly
if (anotherComparator == this) 
return true;

return false;
}
...

[Abdul Mohsin]

Thanks Bill and Joanne for your help and also for pointing out my silly mistake.