DATE AND TIME

** DATE AND TIME does NOT use NEW to create objects
We use "of" and "parse"

yyyy-MM-dd is the default format for dates
HH mm ss is the default formate for time
YYYY-MM-DDTHH:mm:ss is the default format for time/date

===============================================================

Date only - LocalDate

===============================================================

Using the static method "of" to create a date object

METHOD ANALYSIS TABLE
---------------------
name: of
class: LocalDate
static
parameters: 3 integers - yyyy-MM-dd  // no leading zeros
return type: void
description: Creating a date object using LocalDate
example: theDate1 = LocalDate.of(2020, 6, 9);

=======================================================

// date first 1

import java.time.LocalDate;

public class DateAndTime1 {

   public static void main(String[]args) {
   
      LocalDate theDate1 = null;
      
	  // three integer parameters - no leading zeros
      theDate1 = LocalDate.of(2020, 6, 9); // "of" is a static method of the LocalDate class
      
      System.out.println(theDate1);

   }

}
=======================================================

// date first 1B

import java.time.LocalDate;

public class DateAndTime1B {

   public static void main(String[]args) {
   
      LocalDate theDate1 = null;  // works
      
      LocalDate theDate2 = new LocalDate();  // does not work

   }

}

===============================================================


// date first 1C - overview. Null, using of, using parse, using DateTimeFormatter

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

public class DateAndTime1C {

   public static void main(String[]args) {
   
      LocalDate theDate1 = null;  // works
      
      // LocalDate theDate2 = new LocalDate();  // does not work
      
      LocalDate theDate2 = LocalDate.of(2020, 2, 2);
      LocalDate theDate3 = LocalDate.parse("2020-02-02");
      LocalDate theDate4 = LocalDate.parse("19 Feb 2020", DateTimeFormatter.ofPattern("dd MMM yyyy"));
      
      System.out.println(theDate1);
      System.out.println(theDate2);
      System.out.println(theDate3);
      System.out.println(theDate4);

   }

}

OUTPUT

 ----jGRASP exec: java DateAndTime2
null
2020-02-02
2020-02-02
2020-02-19

 ----jGRASP: operation complete.


=============================================================

The role of "toString" with any created object

=============================================================

// date 2

import java.time.LocalDate;

public class DateAndTime2 {

   public static void main(String[]args) {
   
      LocalDate theDate1 = null;
      
      theDate1 = LocalDate.of(2020, 6, 9);  // created object
      
      // does not work as year, month and day properties are private
      // System.out.println(theDate1.year); 
      // System.out.println(theDate1.month);
      // System.out.println(theDate1.day);
	  
	  // The toString works because this is a public method
	  // toString is the way to get the private properties "out"
	  // Being string these values are not a security risk
	  System.out.println(theDate1.toString());
   }

}

OUTPUT

 ----jGRASP exec: java DateAndTime3
2020-06-09

 ----jGRASP: operation complete.


=========================================================

The getters methods. (Accessor methods)

=========================================================

// date 3
// 
// getDayOfMonth
// getDayOfWeek
// getDayOfYear
// getMonthValue
// getMonth
// getYear
// 
// getHour
// getMinutes
// getSecond
// getNano

import java.time.LocalDate;

public class DateAndTime3 {

   public static void main(String[]args) {
   
      LocalDate theDate1 = null;
      
      theDate1 = LocalDate.of(2020, 6, 9);
      
      System.out.println(theDate1);
      System.out.println(theDate1.getYear()); // 2020
      System.out.println(theDate1.getMonth());  // JUNE
      System.out.println(theDate1.getDayOfMonth()); // 9
      System.out.println(theDate1.getDayOfWeek());  // TUESDAY
      System.out.println(theDate1.getDayOfYear());  // 161
   }

}

=============================================================

// date 4

import java.time.LocalDate;

public class DateAndTime4 {

   public static void main(String[]args) {
   
      LocalDate theDate1 = null;
      
      theDate1 = LocalDate.of(1, 6, 9);
      
      // Goes all the way back to year one
      System.out.println(theDate1);
      System.out.println(theDate1.getYear()); // 1
      System.out.println(theDate1.getMonth());  // JUNE
      System.out.println(theDate1.getDayOfMonth()); // 9
      System.out.println(theDate1.getDayOfWeek());  // SATURDAY
      System.out.println(theDate1.getDayOfYear());  // 160
   }

}

===============================================================

// date 5

import java.time.LocalDate;

public class DateAndTime5 {

   public static void main(String[]args) {
   
      LocalDate theDate1 = null;
      
      theDate1 = LocalDate.of(-100000, 6, 9);
      
      // Goes all the way back to year one and beyond
      System.out.println(theDate1);
      System.out.println(theDate1.getYear()); // -100000
      System.out.println(theDate1.getMonth());  // JUNE
      System.out.println(theDate1.getDayOfMonth()); // 9
      System.out.println(theDate1.getDayOfWeek());  // SATURDAY
      System.out.println(theDate1.getDayOfYear());  // 160
   }

}
============================================================

Using the static method "of" to create a date object

============================================================

METHOD ANALYSIS TABLE
---------------------
name: of
class: LocalDate
static
parameters: 3 integers - yyyy-MM-dd
return type: void
description: Creating a date object using LocalDate
example: theDate1 = LocalDate.of(2020, 6, 9);

=======================================================

Using the static method "parse" to create a date object

=======================================================

yyyy-MM-dd

Using the static method "parse" to create a date object

METHOD ANALYSIS TABLE
---------------------
name: parse
class: LocalDate
static
parameters: 1) one string, 2) one string with DateTimeFormatter.ofPattern
return type: void
description: Creating a date object using LocalDate
example: theDate1 = LocalDate.parse("2020-08-12");  // follow exact template


=========================================================

// date 6

import java.time.LocalDate;

public class DateAndTime6 {

   public static void main(String[]args) {
   
      LocalDate theDate1 = null;
      
	  // one string yyyy-MM-dd
      theDate1 = LocalDate.parse("2020-06-04"); // parse is a static method of the LocalDate class
      
      System.out.println(theDate1);

   }

}
==============================================================================

Starting with a different date format - use "DateTimeFormatter.ofPattern"

==============================================================================

// date 7

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

public class DateAndTime7 {

   public static void main(String[]args) {
   
      LocalDate theDate1 = null;
      
	 // two arguements - 
	 // 1) the date
     // 2) the explanation of the date format using ofPattern method
     // ofPattern is a static method of the DateTimeFormatter class
     // MMM means the month Jun (not JUN), Jan (not JAN)
     // MM means the number of the month
	 // Feb 31 will yeild an output of Feb 28
	 // Feb 32 and the program will crash with a DateTimeException
	 
		theDate1 = LocalDate.parse("2021-06-01", DateTimeFormatter.ofPattern("yyyy-MM-dd"));
		System.out.println(theDate1);
		
		theDate1 = LocalDate.parse("01/12/2019", DateTimeFormatter.ofPattern("dd/MM/yyyy"));
		System.out.println(theDate1);
		
		theDate1 = LocalDate.parse("04-Jun-2018", DateTimeFormatter.ofPattern("dd-MMM-yyyy"));
		System.out.println(theDate1);
		
		theDate1 = LocalDate.parse("Jun 27, 2019", DateTimeFormatter.ofPattern("MMM dd, yyyy"));
		System.out.println(theDate1);

   }

}

OUTPUT

 ----jGRASP exec: java DateAndTime
2021-06-01
2019-12-01
2018-06-04
2019-06-27

 ----jGRASP: operation complete.

================================================================================

Changeing the date format later - use "DateTimeFormatter.ofPattern"
Non-static so we must first create a DateTimeFormatter object

================================================================================

METHOD ANALYSIS TABLE
---------------------
name: format
class: DateTimeFormatter
non static
parameters: one
return type: String
description: Changing the appearance of an existing date object
example: String newDateFormat = dmy.format(theDate2);


// date 8

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

public class DateAndTime8 {

   public static void main(String[]args) {

      
      LocalDate theDate2 = LocalDate.of(2020, 2, 2);
      
      System.out.println(theDate2);
      
      // To change the date format we use the Non static "format" method
      // Therefore we need a DateTimeFormatter object
	  // Do not use "new" to create this object
      DateTimeFormatter dmy = DateTimeFormatter.ofPattern("dd-MM-yyyy");
      String newDateFormat = dmy.format(theDate2);
      
      System.out.println(newDateFormat);
      
   }

}
======================================================================================

Current date, current time, current date and time together

======================================================================================


// date 9

import java.time.LocalDate;
import java.time.LocalTime;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class DateAndTime9 {

   public static void main(String[]args) {

      LocalDate date1 = LocalDate.now();
      System.out.println(date1);
      
      LocalTime time1 = LocalTime.now();
      System.out.println(time1);
      
      LocalDateTime dateTime1 = LocalDateTime.now();
      System.out.println(dateTime1);

      // parsing the time to a String for further processing later
      String theNumber = "" + time1;
      System.out.println(theNumber);
      
   }

}

OUTPUT

 ---- jGRASP exec: java DateAndTime8
2022-11-25
11:03:03.576
2022-11-25T11:03:03.576
11:03:03.576

 ----jGRASP: operation complete.

=====================================================================

Time only - LocalDate

=====================================================================

HH mm ss is the default format for time

// time 1

import java.time.LocalTime;

public class Time1 {

   public static void main(String[]args) {
   
      LocalTime theTime1, theTime2 = null;
      
	  // four integer parameters
     // hour, minute, second, nano
      theTime1 = LocalTime.of(3, 4, 5, 6); // "of" is a static method of the LocalTime class
      theTime2 = LocalTime.of(3, 4);
      
      System.out.println(theTime1);
      System.out.println(theTime2);
   }
}

OUTPUT

 ----jGRASP exec: java Time1
03:04:05.000000006
03:04

 ----jGRASP: operation complete.
 
 ==========================================================================
 
 METHOD ANALYSIS TABLE
---------------------
name: of
class: LocalTime
static
parameters: 4 integers - hour, min, sec, nano
return type: void
description: Creating a time object using LocalTime
example: theTime1 = LocalTime.of(3, 4, 5, 6);

===========================================================================

// time 2  - overview. Null, using of, using parse, using DateTimeFormatter

import java.time.LocalTime;
import java.time.format.DateTimeFormatter;

public class Time2 {

   public static void main(String[]args) {
   
      LocalTime theTime1 = null;
      
      LocalTime theTime2 = LocalTime.of(23, 59, 35, 234);
      // LocalTime theTime3 = LocalTime.parse("23 59 35 234"); second arguement is needed
      LocalTime theTime4 = LocalTime.parse("23 59 35", DateTimeFormatter.ofPattern("HH mm ss"));
    
      System.out.println(theTime1);
      System.out.println(theTime2);
      System.out.println(theTime4);
   }

}

OUTPUT

 ----jGRASP exec: java Time3
null
23:59:35.000000234
23:59:35

 ----jGRASP: operation complete.
 
======================================================================

Date and time together - LocalDateTime

======================================================================

YYYY-MM-DDTHH:mm:ss is the default format for time/date

// Date and time together1

import java.time.LocalDateTime;

public class DateAndTime1 {

   public static void main(String[]args) {
   
      LocalDateTime theDate1 = null;
      // 7 arguements - year, month, day, hour, minutes, seconds, naonseconds
      LocalDateTime theDate2 = LocalDateTime.of(2020, 2, 2, 23, 41, 16, 987);
      LocalDateTime theDate3 = LocalDateTime.parse("2020-02-02T23:41:16"); // cannot parse nano
      
      System.out.println(theDate1);
      System.out.println(theDate2);
      System.out.println(theDate3);
      
      System.out.println(theDate2.toString());
   }
}

OUTPUT

 ----jGRASP exec: java DateAndTime4
null
2020-02-02T23:41:16.000000987
2020-02-02T23:41:16
2020-02-02T23:41:16.000000987

 ----jGRASP: operation complete.
 
 ========================================================================
 
 Doing maths - More on getter methods
 
 ========================================================================
 
// Date and time getter methods 2
// 
// getDayOfMonth
// getDayOfWeek
// getDayOfYear
// getMonthValue
// getMonth
// getYear
// 
// getHour
// getMinutes
// getSecond
// getNano

import java.time.LocalDate;
import java.lang.Math;

public class DateAndTime2 {

   public static void main(String[]args) {
   
      LocalDate theDate1 = null, theDate2 = null;
      theDate1 = LocalDate.of(2018, 6, 9);
      theDate2 = LocalDate.of(2020, 6, 9);
      
      System.out.println(theDate1);
      
      // maths is possible when the values are stored as numbers
      int year1 = theDate1.getYear();
      int year2 = theDate2.getYear();
      int month1 = theDate1.getMonthValue(); // the value, not the name
      int month2 = theDate1.getMonthValue();
      
      // Always want the difference to be a positive number
      System.out.println("The year difference is " + Math.abs(year1 - year2));
      System.out.println("The month difference is " + Math.abs(month1 - month2));
   }

}

OUTPUT

 ----jGRASP exec: java DateAndTime5
2018-06-09
The year difference is 2
The month difference is 0

 ----jGRASP: operation complete.
 
 ========================================================================
 
 Doing maths - is equal, is before, is after
 
 ========================================================================
 
 METHOD ANALYSIS TABLE
---------------------
name: isBefore
class: LocalTime
static
parameters: one (date object)
return type: boolean
description: Determines if one date is before another
example: date2.isBefore(date1)

========================================================================
 
 // date time 5
 // date calculations - is before, is equal, is after
 // "isBefore" is used in the bubble sort algorithm to sort dates

import java.time.LocalDate;

public class DateAndTime5 {

   public static void main(String[]args) {
   
      LocalDate[] dateArray = new LocalDate[5];
      LocalDate temp = LocalDate.of(1, 1, 1);
      dateArray[0] = LocalDate.of(2020, 8, 12);
      dateArray[1] = LocalDate.of(2019, 10, 29);
      dateArray[2] = LocalDate.of(2019, 1, 8);
      dateArray[3] = LocalDate.of(2020, 12, 6);
      dateArray[4] = LocalDate.of(2020, 7, 12);
	  
      System.out.println("Original order");
      for(int i = 0; i < 5; i++)
         System.out.println(dateArray[i]);
         
      // bubble sort algorithm   
      for(int i = 0; i < 5;i++) {
         for(int k = i + 1; k < 5; k++){
            LocalDate date1 = dateArray[i];
            LocalDate date2 = dateArray[k];
            
            // isBefore returns boolean
            if(date2.isBefore(date1)) {
               temp = dateArray[i];
               dateArray[i] = dateArray[k];
               dateArray[k] = temp;
            } // end if 
         } // inner loop
      } // outer loop
      
      System.out.println("Sorted Array oldest to newest");
      for(int i = 0; i < 5; i++)
         System.out.println(dateArray[i]);
   }
}

OUTPUT

 ----jGRASP exec: java DateAndTime5
Original order
2020-08-12
2019-10-29
2019-01-08
2020-12-06
2020-07-12
Sorted Array oldest to newest
2019-01-08
2019-10-29
2020-07-12
2020-08-12
2020-12-06

 ----jGRASP: operation complete.
 
 =================================================================
 
 Adding and subtracting days, weeks, months and years
 
 =================================================================
 
// Date and time calculations 6
// plusYears
// plusMonths
// plusDays
// plusWeeks
// 
// minusYears
// minusMonths
// minusDays
// minusWeeks


import java.time.LocalDate;
import java.lang.Math;

public class DateAndTime6 {

   public static void main(String[]args) {
   
      LocalDate startFast = LocalDate.of(2021, 6, 9);
      LocalDate endFast = startFast.plusDays(40);
     
      System.out.println("Start Fast: " + startFast); 
      System.out.println("End Fast: " + endFast);
      
      LocalDate startHomeLoan = LocalDate.of(2021, 6, 9);
      LocalDate endHomeLoan = startFast.plusYears(20);
     
      System.out.println("Start Home Loan: " + startHomeLoan); 
      System.out.println("End Home Loan: " + endHomeLoan);
      
      LocalDate endCourse = LocalDate.of(2021, 01, 9);
      LocalDate startCourse = startFast.minusWeeks(50);
     
      System.out.println("Started Course: " + startCourse); 
      System.out.println("Ended Course: " + endCourse);
   }
}

OUTPUT

 ----jGRASP exec: java DateAndTime6
 
Start Fast: 2021-06-09
End Fast: 2021-07-19
Start Home Loan: 2021-06-09
End Home Loan: 2041-06-09
Start Course: 2020-06-24
End Course: 2021-01-09

 ----jGRASP: operation complete.
 
 =============================================================================