Introduction to Date and Time in Java

Input/Output and Streams in Java

Alex Liu

Software Development Engineer

Creating Date objects

The LocalDate class
- Represents dates without time
The LocalTime class
- Represents time without date
Import required classes

import java.time.LocalDate;
import java.time.LocalTime;

Creating Date objects(continued)

Retrieve current date and time using .now()

LocalDate date = LocalDate.now();
LocalTime time = LocalTime.now();
System.out.println(date);
System.out.println(time);

(Note: The time will vary based on when the program is executed)

2025-03-10
12:45:30.123456

Formatting Dates in Java

DateTimeFormatter
- Define custom date formats
- Supports multiple patterns like yyyy-MM-dd, MM/dd/yyyy

Import necessary classes

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

Formatting Dates in Java(continued)

Create a LocalDate instance date

LocalDate date = LocalDate.now(); // Current format we have will be: `2025-03-10`

Create a DateTimeFormatter with the pattern MM/dd/yyyy using .ofPattern()

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("MM/dd/yyyy");

Apply the DateTimeFormatter using .format() method

System.out.println(date.format(formatter))

03/10/2025

Parsing String into Date

Using LocalDate.parse() to converts text to a date
- Ensure the format matches the input string

Use .parse() with a text in yyyy-MM-dd format to parse into a Date object

LocalDate parsedDate = LocalDate.parse("2024-03-10");
System.out.println(parsedDate);

Print the Date object will output:
```
2024-03-10
```

Performing Date adjustment

Use .plusDays() and .minusDays() to adjust dates

LocalDate date = LocalDate.now();
// Current value:
System.out.println(date); 
// Apply `.plusDays()` with value `7`
LocalDate futureDate = date.plusDays(7);
// Value after adjustment
System.out.println(futureDate);

2025-03-10
2025-03-17

Performing Date adjustment(continued)

Apply .minusDays() with value 7

LocalDate pastDate = date.minusDays(7);
System.out.println(pastDate);

Current value for pastDate:
```
2025-03-03
```

Summary

LocalDate and LocalTime manage dates and times separately
- Note: The time will vary based on when the program is executed
- .parse() can converts text to a date
- .now() retrieves the current date/time
DateTimeFormatter formats and parses dates
- define custom date formats
- Supports multiple patterns like yyyy-MM-dd, MM/dd/yyyy
Perform date calculations using .plusDays() and .minusDays()`

Let's practice!

Input/Output and Streams in Java