Java Date and Calendar Class.

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Get the Current Date:

Date today = new Date();
System.out.println(“Current date: “ + today);
OUTPUT:
date: Sat May 04 02:29:59 IST 2019

Difference between dates:

Date currentTime = new Date(); Thread.sleep(3000); //Waits for 3 seconds. Date newTime = new Date();
//diferrence in ms. long msDelay = newTime.getTime() – currentTime.getTime();

Check Whether Time Interval has Passed:

public static void main(String[] args) throws Exception { Date startTime = new Date(); long deadLine = startTime.getTime() + 3000; // +3 seconds
Date deadLineDate = new Date(deadLine); Date currentTime = new Date();
int secondsCount = 0;
while(!currentTime.after(deadLineDate))// Check whether currentTime is after deadLineDate {
Thread.sleep(1000); // Sleep for 1 sec.
secondsCount++;
System.out.println(secondsCount + ” seconds have passed.”);
currentTime = new Date();
}
System.out.println(“Reached DeadLine!”);}

Output:
1 seconds have passed. 2 seconds have passed. 3 seconds have passed. Reached DeadLine!

Using getTime()
public class Main { public static void main(String[] args) {


 Date startTime = new Date();

long deadLine = startTime.getTime() + 3000; // +3 seconds
Date deadLineDate = new Date(deadLine); Date currentTime = new Date();
int secondsCount = 0;
while(currentTime.getTime() < deadLineDate.getTime())// Check whether currentTime is after deadLineDate {
Thread.sleep(1000); // Sleep for 1 sec.
secondsCount++;
System.out.println(secondsCount + ” seconds have passed.”);
currentTime = new Date();
}
System.out.println(“Reached DeadLine!”);

}}

before()
equals()
also work with same syntax as after()

Various get and set methods:

get methods
Date currentTime = new Date();int hours = currentTime.getHours(); // hours passed since midnight. 
int mins = currentTime.getMinutes(); // hours passed since midnight.int secs = currentTime.getSeconds(); // seconds passed since midnight.

set methods
Date yearStartTime = new Date(); 
yearStartTime.setHours(0); 
yearStartTime.setMinutes(0); 
yearStartTime.setSeconds(0); 
yearStartTime.setDate(1); // First day of month
yearStartTime.setMonth(0); // January (months are indexed from 0 to 11)

Calendar class:

Calendar calendar = new GregorianCalendar(2017, 0 , 25);
GregorianCalendar calendar = new GregorianCalendar(2017, Calendar.JANUARY , 25);

set the time 10:30:15 1 Jan 2019

public static void main(String[] args) { Calendar calendar = new GregorianCalendar(); calendar.set(Calendar.YEAR, 2019); calendar.set(Calendar.MONTH, 0); calendar.set(Calendar.DAY_OF_MONTH, 1); calendar.set(Calendar.HOUR_OF_DAY, 10); calendar.set(Calendar.MINUTE, 30); calendar.set(Calendar.SECOND, 15); System.out.println(calendar.getTime());}

Output:

Tue Jan 01 10:30:15 IST 2019
—————————————————————-

public static void main(String[] args) { Calendar calendar = new GregorianCalendar(2019, Calendar.JANUARY , 1); calendar.set(Calendar.HOUR, 10); calendar.set(Calendar.MINUTE, 30); calendar.set(Calendar.SECOND, 15); calendar.add(Calendar.MONTH, –2); // Date will automatically adjust into 2018. System.out.println(calendar.getTime());}

output:
Thu Nov 01 10:30:15 IST 2018
——————————————————————
roll() : This method will make change only in particular part, In this example
only Month will be reduced to Nov but years and other time will not be changed.

public static void main(String[] args) { Calendar calendar = new GregorianCalendar(2019, Calendar.JANUARY , 1); calendar.set(Calendar.HOUR, 10); calendar.set(Calendar.MINUTE, 30); calendar.set(Calendar.SECOND, 15); calendar.roll(Calendar.MONTH, –2); // Date will automatically adjust into 2018. System.out.println(calendar.getTime());}
Output:
Fri Nov 01 10:30:15 IST 2019
——————————————————————

get and set:

calendar.set(Calendar.HOUR, 10);calendar.set(Calendar.MINUTE, 30);calendar.set(Calendar.SECOND, 15); System.out.println(“Year: “ + calendar.get(Calendar.YEAR));System.out.println(“Month: “ + calendar.get(Calendar.MONTH));
——————————————————————-

date format:

SimpleDateFormat dateFormat = new SimpleDateFormat(“EEEE, MMMM d, yyyy”);
Calendar calendar = new GregorianCalendar(2019, Calendar.JANUARY , 1);
System.out.println(dateFormat.format(calendar.getTime()));

output:
Tuesday, January 1, 2019

Difference of days between two dates:

long diff_ms = date1.getTime() – date2.getTime();
days = diff_ms / (24 * 60 * 60 * 1000);


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Published by Abhishek

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