Java date-time method

Java date-time method

The method names in the Java Date-Time API are as consistent as possible between classes.

For example, now method returns the date or time value of the current moment. from method allows you to convert from one class to another.

The following table lists common prefixes:

• of
  Static factory method
  The factory method creates an instance and validates the input parameters
• from
  The static factory method converts input parameters to instances of the target class.
• parse
  Static factory method
  Resolve the input string to create an instance of the target class.
• format
  The instance method
  Format temporary objects to produce strings.
• get
  The instance method
  Returns a portion of the target object.
• is
  The instance method
  Query the target object.
• with
  The instance method
  Returns a copy of the target object for which an element has changed.
• plus
  The instance method
  Returns a copy of the object with the amount of time added.
• minus
  The instance method
  Returns a copy of the object with the amount of time subtracted.
• to
  The instance method
  Convert this object to another type.
• at
  The instance method
  Combine this object with another object.

Of() method

The XXX() method of the Java Date Time API is used to create objects.

The following code shows how to create objects for the LocalDate class:

import java.time.LocalDate;
import java.time.Month;

public class Main {
  public static void main(String[] args) {
    LocalDate localDate1  = LocalDate.of(2014, 5, 21); 
    System.out.println(localDate1);
    
    LocalDate localDate2  = LocalDate.of(2014, Month.MARCH, 4);
    System.out.println(localDate2);
    
    LocalDate localDate3  = LocalDate.ofEpochDay(2014);
    System.out.println(localDate3);
    
    LocalDate localDate4  = LocalDate.ofYearDay(2014, 39);
    System.out.println(localDate4);
  }
}

The code above produces the following results.

From() method

from() is a static factory method that derives datetime objects from specified parameters.

Unlike of() from() data conversion of the specified parameters.

The following code shows how to derive LocalDate from LocalDateTime:

import java.time.LocalDate;
import java.time.LocalDateTime;

public class Main {
  public static void main(String[] args) {
    LocalDateTime  localDateTime = LocalDateTime.of(2015, 6,  21,  13, 40);
    System.out.println(localDateTime);
    
    LocalDate localDate  = LocalDate.from(localDateTime);
    System.out.println(localDate);
  }
}

The code above produces the following results.

With() method

To change the fields in the datetime object, we can use a method with a prefix.

The withXXX() method returns a copy of an object, and the specified field has changed because most objects in the Date Time API are imm changed.

The following code shows how to get LocalDate from another LocalDate and change the year:

import java.time.LocalDate;
import java.time.Month;

public class Main {
  public static void main(String[] args) {
    LocalDate localDate1  = LocalDate.of(2014, Month.MAY,  2);
    System.out.println(localDate1);
    
    LocalDate localDate2  = localDate1.withYear(2015);
    System.out.println(localDate2);
    
    LocalDate localDate3  = localDate1.withYear(2014).withMonth(7);
    System.out.println(localDate3);
    
  }
}

The code above produces the following results.

GetXXX() method

getXXX() specified element of the object.

The following code shows how to LocalDate and days from the LocalDate object:

import java.time.LocalDate;
import java.time.Month;

public class Main {
  public static void main(String[] args) {
    LocalDate localDate = LocalDate.of(2014, 6, 21);
    int year = localDate.getYear();
    System.out.println(year);
    Month month = localDate.getMonth();
    System.out.println(month);

    int day = localDate.getDayOfMonth();
    System.out.println(day);

  }
}

The code above produces the following results.

ToXXX() method

toXXX() objects to related types.

The following code shows some examples of using the toXXX() method.

import java.time.LocalDate;

public class Main {
  public static void main(String[] args) {
    LocalDate localDate = LocalDate.of(2014, 6, 21); 
    long days = localDate.toEpochDay(); 
    System.out.println(days);

  }
}

The code above produces the following results.

AtXXX() method

atXXX() a new datetime object from an existing datetime object with additional information.

The following code is used in methods to add additional information to the date object.

import java.time.LocalDate;
import java.time.LocalDateTime;

public class Main {
  public static void main(String[] args) {
    LocalDate localDate  = LocalDate.of(2014, 6, 21);
    System.out.println(localDate);

    LocalDateTime  localTime1 = localDate.atStartOfDay();
    System.out.println(localTime1);

    LocalDateTime  localTime2 = localDate.atTime(16, 21);
    System.out.println(localTime2);
  }
}

The code above produces the following results.

The following code shows how to use the atXXX() method of building local dates using the support builder pattern:

import java.time.LocalDate;
import java.time.Year;

public class Main {
  public static void main(String[] args) {
    LocalDate localDate  = Year.of(2014).atMonth(6).atDay(21);
    System.out.println(localDate);

  }
}

The code above produces the following results.

PlusXXX() method

plusXXX() a copy of the object by adding the specified value.

The following code shows how to use the plus method to add more time date objects locally.

import java.time.LocalDate;

public class Main {
  public static void main(String[] args) {
    LocalDate localDate  = LocalDate.of(2014, 6, 21); 
    LocalDate localDate1  = localDate.plusDays(5);   
    System.out.println(localDate1);
    LocalDate localDate2  = localDate.plusMonths(3);
    System.out.println(localDate2);
    LocalDate localDate3  = localDate.plusWeeks(3);        
    System.out.println(localDate3);
  }
}

The code above produces the following results.

minusXXX() method

minusXXX() a copy of the object by subtracting the specified value.

The following code shows how to subtract time from the local date object.

import java.time.LocalDate;

public class Main {
  public static void main(String[] args) {
    LocalDate localDate  = LocalDate.of(2014, 6, 21); 
    LocalDate localDate1  = localDate.minusMonths(5);   
    System.out.println(localDate1);
    LocalDate localDate2  = localDate.minusWeeks(3);
    System.out.println(localDate2);
  }
}

The code above produces the following results.

Now() method

The now() method returns the current time of various classes, such as LocalDate, LocalTime, LocalDateTime, ZonedDateTime.

The following code shows how to use the now() method to return the current date and time.

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.ZonedDateTime;

public class Main {
  public static void main(String[] args) {
    LocalDate localDate = LocalDate.now(); 
    System.out.println(localDate);
    
    LocalTime  localTime  = LocalTime.now();
    System.out.println(localTime);
    
    LocalDateTime  dateTime  = LocalDateTime.now();
    System.out.println(dateTime);
    
    ZonedDateTime dateTimeWithZone  = ZonedDateTime.now();
    System.out.println(dateTimeWithZone);
  }
}

The code above produces the following results.