Core Java - DateAPIJava provides the Date class available in java.util package, this class encapsulates the current date and time. The Date class supports two constructors. The first constructor initializes the object with the current date and time
Date()
The following constructor accepts one argument that equals the number of milliseconds that have elapsed since
midnight, January 1, 1970
Date(long millisec)
Once you have a Date object available, you can call any of the following support methods to play with dates:
S.No Methods Description
---- ---------------------------- ----------------------------------------------------------------------------------
1 boolean after(Date date) Returns true if the invoking Date object contains a date that is later than the
one specified by date, otherwise,it returns false.
2 boolean before(Date date) Returns true if the invoking Date object contains a date that is earlier than the
one specified by date,otherwise, it returns false.
3 Object clone( ) Duplicates the invoking Date object.
4 int compareTo(Date date) Compares the value of the invoking object with that of date. Returns 0 if the values
are equal. Returns a negative value if the invoking object is earlier than date.
Returns a positive value if the invoking object is later than date.
5 int compareTo(Object obj) Operates identically to compareTo(Date) if obj is of class Date. Otherwise, it throws
a ClassCastException.
6 boolean equals(Object date) Returns true if the invoking Date object contains the same time and date as the one
specified by date, otherwise, it returns false.
7 long getTime( ) Returns the number of milliseconds that have elapsed since January 1, 1970.
8 int hashCode( ) Returns a hash code for the invoking object.
9 void setTime(long time) Sets the time and date as specified by time, which represents an elapsed time in
milliseconds from midnight, January 1, 1970.
10 String toString( ) Converts the invoking Date object into a string and returns the result.
Getting Current Date & Time : This is very easy to get current date and time in Java. You can use a simple Date object with toString()method to print current date and time as follows:
import java.util.Date;
public class DateDemo{
public static void main(String args[]){
// Instantiate a Date object
Date date =new Date();
// display time and date using toString()
System.out.println(date.toString());
}
}
Output : Wed Dec 27 15:21:16 IST 2023 Date Comparison : There are following three ways to compare two dates: Date Formatting using SimpleDateFormat : SimpleDateFormat is a concrete class for formatting and parsing dates in a locale-sensitive manner. SimpleDateFormat allows you to start by choosing any user-defined patterns for date-time formatting.
import java.util.*;
import java.text.*;
public class DateDemo{
public static void main(String args[]){
Date dNow =new Date();
SimpleDateFormat ft = new SimpleDateFormat("E yyyy.MM.dd 'at' hh:mm:ss a zzz");
System.out.println("Current Date : "+ ft.format(dNow));
}
}
Output : Current Date : Wed 2023.12.27 at 03:23:43 PM IST Simple DateFormat format codes : To specify the time format, use a time pattern string. In this pattern, all ASCII letters are reserved as pattern letters, which are defined as the following:
Character Description Example
--------- ----------------------------- --------------------------
G Era designator AD
Y Year in four digits 2001
M Month in year July or 07
D Day in month 10
H Hour in A.M./P.M. (1~12) 12
H Hour in day (0~23) 22
M Minute in hour 60
S Second in minute 55
S Millisecond 234
E Day in week Tuesday
D Day in year 360
F Day of week in month 2 (second Wed. in July)
W Week in year 40
W Week in month 1
A A.M./P.M. marker PM
K Hour in day (1~24) 24
K Hour in A.M./P.M. (0~11) 10
Z Time zone Eastern Standard Time
' Escape for text Delimiter
" Single quote `
Date Formatting using printf : Date and time formatting can be done very easily using printf method. You use a two-letter format, starting with t and ending in one of the letters of the table given below. Eg:
import java.util.Date;
public class DateDemo{
public static void main(String args[]){
// Instantiate a Date object
Date date =new Date();
// display time and date using toString()
String str =String.format("Current Date/Time : %tc", date );
System.out.printf(str);
}
}
Output : Current Date/Time : Wed Dec 27 15:37:26 IST 2023 It would be a bit silly if you had to supply the date multiple times to format each part. For that reason, a format string can indicate the index of the argument to be formatted. The index must immediately follow the % and it must be terminated by a $. Eg:
import java.util.Date;
public class DateDemo{
public static void main(String args[]){
// Instantiate a Date object
Date date =new Date();
// display time and date using toString()
System.out.printf("%1$s %2$tB %2$td, %2$tY","Due date:", date);
}
}
Output : Due date: December 27, 2023 Alternatively, you can use the < flag. It indicates that the same argument as in the preceding format specification should be used again. Eg:
import java.util.Date;
public class DateDemo{
public static void main(String args[]){
// Instantiate a Date object
Date date =new Date();
// display formatted date
System.out.printf("%s %tB %
Output : Due date: December 27, 2023 Date and Time Conversion Characters :
Character Description Example
--------- -------------------------------------------------- -------------------------------
c Complete date and time Mon May 04 09:51:52 CDT 2009
F ISO 8601 date 2004-02-09
D U.S. formatted date (month/day/year) 02/09/2004
T 24-hour time 18:05:19
r 12-hour time 06:05:19 pm
R 24-hour time, no seconds 18:05
Y Four-digit year (with leading zeroes) 2004
y Last two digits of the year (with leading zeroes) 04
C First two digits of the year (with leading zeroes) 20
B Full month name February
b Abbreviated month name Feb
m Two-digit month (with leading zeroes) 02
d Two-digit day (with leading zeroes) 03
e Two-digit day (without leading zeroes) 9
A Full weekday name Monday
a Abbreviated weekday name Mon
j Three-digit day of year (with leading zeroes) 069
H Two-digit hour (with leading zeroes), between 00 and 23 18
k Two-digit hour (without leading zeroes), between 0 and 23 18
I Two-digit hour (with leading zeroes), between 01 and 12 06
l Two-digit hour (without leading zeroes), between 1 and 12 6
M Two-digit minutes (with leading zeroes) 05
S Two-digit seconds (with leading zeroes) 19
L Three-digit milliseconds (with leading zeroes) 047
N Nine-digit nanoseconds (with leading zeroes) 047000000
P Uppercase morning or afternoon marker PM
p Lowercase morning or afternoon marker pm
z RFC 822 numeric offset from GMT -0800
Z Time zone PST
s Seconds since 1970-01-01 00:00:00 GMT 1078884319
Q Milliseconds since 1970-01-01 00:00:00 GMT 1078884319047
There are other useful classes related to Date and time. For more details, you can refer to Java Standard
documentation.Parsing Strings into Dates : The SimpleDateFormat class has some additional methods, notably parse( ) , which tries to parse a string according to the format stored in the given SimpleDateFormat object. Eg:
import java.util.*;
import java.text.*;
public class DateDemo{
public static void main(String args[]){
SimpleDateFormat ft =new SimpleDateFormat("yyyy-MM-dd");
String input = args.length ==0?"2023-12-27": args[0];
System.out.print(input +" Parses as ");
Date t;
try{
t = ft.parse(input);
System.out.println(t);
}catch(Exception e){
System.out.println("Unparseable using "+ ft);
}
}
}
Output : 2023-12-27 Parses as Wed Dec 27 00:00:00 IST 2023 Sleeping for a While : You can sleep for any period of time from one millisecond up to the lifetime of your computer. For example, following program would sleep for 10 seconds:
import java.util.*;
public class SleepDemo{
public static void main(String args[]){
try{
System.out.println(new Date()+"\n");
Thread.sleep(5*60*10);
System.out.println(new Date()+"\n");
}catch(Exception e){
System.out.println("Got an exception!");
}
}
}
Output : Wed Dec 27 15:56:31 IST 2023 Wed Dec 27 15:56:34 IST 2023 Measuring Elapsed Time : Sometimes, you may need to measure point in time in milliseconds. So let's rewrite above example once again:
import java.util.*;
public class DiffDemo{
public static void main(String args[]){
try{
long start =System.currentTimeMillis();
System.out.println(new Date()+"\n");
Thread.sleep(5*60*10);
System.out.println(new Date()+"\n");
long end=System.currentTimeMillis();
long diff =end- start;
System.out.println("Difference is : "+ diff);
}catch(Exception e){
System.out.println("Got an exception!");
}
}
}
Output : Wed Dec 27 15:58:42 IST 2023 Wed Dec 27 15:58:45 IST 2023 Difference is : 3021 « Previous (Core Java -Regex) |