LocalDateTime

18.1.1 Why DateTime Matters

Dates and times are everywhere in real-world apps:

• User sign-up dates

• Order timestamps

• Booking systems

• Log files, audit trails, reports

Before Java 8, the old Date and Calendar APIs were confusing and error-prone.
Java 8 introduced java.time — a modern, safe, and clear date-time framework.

✅ Key idea:
LocalDateTime is an immutable class that combines date + time but no timezone.
For example: 2025-07-03T15:30:00.

Use LocalDateTime when you need:

• A precise timestamp

• No need for timezone math

• A safe, predictable date-time representation

18.1.2 Creating LocalDateTime

You can create a LocalDateTime in multiple ways:

• The current moment

• A specific date-time

• From strings or other time objects

Mini Lab: Basic LocalDateTime

java
import java.time.LocalDateTime;

public class LocalDateTimeMiniLab {
    public static void main(String[] args) {
        // Current date-time
        LocalDateTime now = LocalDateTime.now();
        System.out.println("Now: " + now);

        // Specific date-time
        LocalDateTime birthday = LocalDateTime.of(1990, 5, 15, 10, 30);
        System.out.println("Birthday: " + birthday);

        // Add days, subtract hours
        LocalDateTime nextWeek = now.plusDays(7);
        LocalDateTime yesterday = now.minusHours(24);

        System.out.println("Next week: " + nextWeek);
        System.out.println("Yesterday: " + yesterday);
    }
}

Key points:

• now() returns the current system date-time.

• of() builds a specific one.

• plusDays(), minusHours() create new modified copies — original stays unchanged.