Java LocalDateTime withDayOfYear() Method

The withDayOfYear() method in Java, part of the java.time.LocalDateTime class, is used to return a copy of the LocalDateTime with the day-of-year altered. This method is useful for manipulating date-time values by changing the day of the year while keeping other fields unchanged.

Table of Contents

1. Introduction
2. withDayOfYear() Method Syntax
3. Understanding withDayOfYear()
4. Examples
   • Basic Usage
   • Using withDayOfYear() in Conditional Statements
5. Real-World Use Case
6. Conclusion

Introduction

The withDayOfYear() method allows you to create a new LocalDateTime instance with the specified day of the year. This is particularly useful when you need to adjust the day of the year while preserving the rest of the date-time fields.

withDayOfYear() Method Syntax

The syntax for the withDayOfYear() method is as follows:

public LocalDateTime withDayOfYear(int dayOfYear)

Parameters:

• dayOfYear: The day of the year to set in the resulting LocalDateTime, from 1 to 365-366 depending on whether it's a leap year.

Returns:

• A LocalDateTime based on this date-time with the specified day of the year, not null.

Throws:

• DateTimeException if the day of the year value is invalid or if the resulting LocalDateTime exceeds the supported date range.

Understanding withDayOfYear()

The withDayOfYear() method creates a new LocalDateTime instance with the specified day of the year while keeping the other fields (year, month, day of month, hour, minute, second, and nanosecond) unchanged.

Examples

Basic Usage

To demonstrate the basic usage of withDayOfYear(), we will change the day of the year of a LocalDateTime instance.

Example

import java.time.LocalDateTime;

public class LocalDateTimeWithDayOfYearExample {
    public static void main(String[] args) {
        LocalDateTime dateTime = LocalDateTime.of(2023, 6, 15, 10, 30);
        LocalDateTime newDateTime = dateTime.withDayOfYear(200); // Change day of year to 200

        System.out.println("Original DateTime: " + dateTime);
        System.out.println("New DateTime: " + newDateTime);
    }
}

Output:

Original DateTime: 2023-06-15T10:30
New DateTime: 2023-07-19T10:30

Using withDayOfYear() in Conditional Statements

This example shows how to use the withDayOfYear() method in conditional statements to perform actions based on the adjusted date-time.

Example

import java.time.LocalDateTime;

public class LocalDateTimeConditionalExample {
    public static void main(String[] args) {
        LocalDateTime dateTime = LocalDateTime.of(2023, 6, 15, 10, 30);
        LocalDateTime newDateTime = dateTime.withDayOfYear(1); // Change day of year to 1

        if (newDateTime.getDayOfYear() == 1) {
            System.out.println("The date has been changed to the first day of the year.");
        } else {
            System.out.println("The date has not been changed to the first day of the year.");
        }
    }
}

Output:

The date has been changed to the first day of the year.

Real-World Use Case

Scheduling Tasks on Specific Days of the Year

In real-world applications, the withDayOfYear() method can be used to schedule tasks or events on specific days of the year.

Example

import java.time.LocalDateTime;

public class TaskSchedulerExample {
    public static void main(String[] args) {
        LocalDateTime taskDateTime = LocalDateTime.of(2023, 6, 15, 10, 30);
        LocalDateTime newTaskDateTime = taskDateTime.withDayOfYear(100); // Schedule task on the 100th day of the year

        System.out.println("Original Task DateTime: " + taskDateTime);
        System.out.println("New Task DateTime: " + newTaskDateTime);
    }
}

Output:

Original Task DateTime: 2023-06-15T10:30
New Task DateTime: 2023-04-10T10:30

Conclusion

The LocalDateTime.withDayOfYear() method is used to create a new LocalDateTime instance with the specified day of the year while keeping other fields unchanged. This method is particularly useful for adjusting the day of the year in date-time calculations. By understanding and using the withDayOfYear() method, you can effectively manage and manipulate date-time data in your Java applications.