Java Date and Time API

Java provides APIs to work with dates and times. Before Java 8, developers used the old Date and Time API. Java 8 introduced a new and improved Date and Time API in the java.time package.

Old Date & Time API

Before Java 8, the following classes were commonly used:

• java.util.Date

• java.sql.Date

Example

java

Date date = new Date();
System.out.println(date);

Output

text

Thu Jul 17 10:30:45 IST 2025

The Date class stores both date and time information.

Limitations of Old API

The old Date and Time API had several drawbacks:

• Date and time are combined in a single object.

• Classes are mutable.

• Formatting is complicated.

• Not thread-safe.

• Difficult to work with date calculations.

SimpleDateFormat

SimpleDateFormat was used to format and parse dates.

Convert Date to String

java

SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");

String formattedDate = sdf.format(new Date());

System.out.println(formattedDate);

Output

java

17/07/2025

Convert String to Date

java

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

Date date = sdf.parse("2022-12-20");

System.out.println(date);

Output

text

Tue Dec 20 00:00:00 IST 2022

Problems with SimpleDateFormat

• Not thread-safe

• Mutable class

• Complex to use

• Can cause issues in multi-threaded applications

Java 8 New Date & Time API

Java 8 introduced the java.time package to overcome the limitations of the old API.

Advantages

• Immutable

• Thread-safe

• Easy to use

• Better API design

• Supports date and time calculations

LocalDate (Date Only)

LocalDate represents only the date (year, month, day).

Example

java

LocalDate date = LocalDate.now();

System.out.println(date);

date = date.plusDays(3);

System.out.println(date);

Check Leap Year

java

boolean leapYear = date.isLeapYear();

System.out.println(leapYear);

LocalTime (Time Only)

LocalTime represents only time.

Example

java

LocalTime time = LocalTime.now();

System.out.println(time);

time = time.plusHours(2);

System.out.println(time);

LocalDateTime (Date and Time)

LocalDateTime represents both date and time.

Example

java

LocalDateTime dateTime = LocalDateTime.now();

System.out.println(dateTime);

Period (Date Difference)

Period is used to calculate the difference between two dates.

Example

java

Period period = Period.between(
        LocalDate.parse("1991-05-20"),
        LocalDate.now());

System.out.println(period);

Output

text

P34Y1M27D

This represents the difference in:

• Years

• Months

• Days

Duration (Time Difference)

Duration is used to calculate the difference between two times.

Example

javaCopy

Duration duration = Duration.between(
        LocalTime.parse("18:00"),
        LocalTime.now());

System.out.println(duration);

Output

text

PT2H30M15S

This represents the difference in:

• Hours

• Minutes

• Seconds

Old API vs New API

Old API

• Mutable

• Not Thread-Safe

• Complex

New API

• Immutable

• Thread-Safe

• Easy to Use

• Built-in Date Calculations

Interview Questions

Why was the new Date and Time API introduced in Java 8?

The old API was mutable, not thread-safe, and difficult to use. Java 8 introduced the java.time package to provide a simpler, immutable, and thread-safe solution.

Is SimpleDateFormat thread-safe?

No, SimpleDateFormat is not thread-safe.

Which classes are commonly used in the Java 8 Date & Time API?

• LocalDate

• LocalTime

• LocalDateTime

• Period

• Duration

Key Points

• Java 8 introduced the java.time package.

• The new API is immutable and thread-safe.

• LocalDate stores only the date.

• LocalTime stores only the time.

• LocalDateTime stores both date and time.

• Period calculates differences between dates.

• Duration calculates differences between times.

• SimpleDateFormat is not thread-safe.

• The new Date & Time API is preferred in modern Java applications.