Java Reference
In-Depth Information
Of course, having modified a
GregorianCalendar
object, you can get the current instant back as a
Date
object using the
getTime()
method that we saw earlier. You can then use a
DateFormat
object to present
this in a readable form.
Comparing Calendars
Checking the relationship between dates represented by
Calendar
objects is a fairly fundamental require-
ment and you have four methods available for comparing them (shown in
Table 15-3
):
TABLE 15-3
:
Methods for Comparing Calendar Objects
METHOD
DESCRIPTION
Returns
true
if the current object corresponds to a time before that of the
Calendar
object
passed as an argument. Note that this implies a
true
return can occur if the date is the same but
the time is different.
before()
Returns
true
if the current object corresponds to a time after that of the
Calendar
object passed
as an argument.
after()
Returns
true
if the current object corresponds to a time that is identical to that of the
Calendar
object passed as an argument.
equals()
Returns a value of type
int
that is negative, zero, or positive depending on whether the time
value for the current object is less than, equal to, or greater than the time value for the argument.
compareTo(Calendar
c)
These are very simple to use. To determine whether the object
thisDate
defines a time that precedes the
time defined by the object
today
, you could write:
if(thisDate.before(today)) {
// Do something...
}
Alternatively you could write the same thing as:
if(today.after(thisDate)) {
// Do something...
}
It's time to look at how we can use calendars.
TRY IT OUT: Using a Calendar
This example deduces important information about when you were born. It uses the
FormattedInput
class from Chapter 8 to get input from the keyboard, so copy this class and the source file for the
Inval-
idUserInputException
class to a new directory for the source files for this example. Here's the code:
import java.util.GregorianCalendar;
import java.text.DateFormatSymbols;
import static java.util.Calendar.*;
