Java Time API - A Code kata

Table of Contents

• What is a Code-Kata
  • How does one go about with this code kata?
    • Simple steps to use this kata
  • Mission
• Requirements
• Project Structure
• Tests Included
  • Java Date Time API
• Solutions
• Take Away

Most, if not all Java developers need to rely on Java date and time libraries.

What is a Code-Kata

A code-kata is a coding exercise that builds muscle memory by a practice of programming to arrive at a known solution.

How does one go about with this code kata?

The essence of the exercise (presentation material and code kata) is to demonstrate the usage patterns for the java API or functionality.

This set of code katas rely on fixing broken tests. The tests may have multiple solutions, the intent is to learn and experiment.

The project contains several JUnit tests that fail.

Simple steps to use this kata

1. Run the test class(es).

2. One or more tests will fail with the test failure message.

3. Fix the failing tests by using HINT and TODO comments.

4. Repeat above steps until all tests pass.

5. Check the solutions to see if there are other ways to solve. (Remember, the solution may be less performant/optimal than yours)

6. Rinse and repeat (delete and checkout again, then back to Step 1) to build muscle memory.

Mission

Your mission, should you choose to accept it, will be to fix the JUnit tests. This message will self-destruct in NaN minutes.

Requirements

How to prepare for coding along

This kata is developed as a Java maven project.Ensure that you have:

1. Apache Maven 3.6.x or above. Tested with Apache Maven 3.6.3. Link: https://maven.apache.org/download.cgi

2. JDK 11 or above. Tested with OpenJDK 11 Link: http://jdk.java.net/11/

3. Your favorite Java IDE. IntelliJ IDEA Ultimate was used to develop this kata.

Project Structure

The structure of the project:

|____pom.xml
|____README.md
|
|____src
| |
| |____test                    <------------------- Kata Tests
| | |____java
| |   |____none
| |     |____cvg
| |       |____datetime
| |
| |____main                    <------------------- Shared ErrorMessages & DemoClass
| | |____java
| |   |____none
| |     |____cvg
| |       |____datetime
| |
| |____solutions               <------------------- Solutions
| | |____java
| |   |____none
| |     |____cvg
| |       |____datetime

Tests Included

Java Date Time API

The JUnit tests listed below are setup to utilize the Java Time API features.

TestKata1InstantAndDateInterop.java

show interoperability between java.util.Date, and the newer java.time.Instant.

TestKata2Clocks.java

show the usage of java.time.Clock.

TestKata3LocalAndZonedDateTimes.java

show the usage of java.time.LocalDate, java.time.LocalTime, java.time.LocalDateTime and java.time.ZonedDateTime.

TestKata4PeriodsAndDurations.java

show the usage of DateTime ranges: Period, Duration tests.

TestKata5DateTimePartials.java

show the usage of DateTime partials: Month, MonthDay, Year, YearMonth and DayOfWeek tests.

TestKata6StreamsInDateTime.java

show the usage of DateTime in Java stream() lazy iterations.

Solutions

Table 1. Solutions for each test:

Kata Test	Solution
TestKata1InstantAndDateInterop.java	TestSolution1InstantAndDateInterop.java
TestKata2Clocks.java	TestSolution2Clocks.java
TestKata3LocalAndZonedDateTimes.java	TestSolution3LocalAndZonedDateTimes.java
TestKata4PeriodsAndDurations.java	TestSolution4PeriodsAndDurations.java
TestKata5DateTimePartials.java	TestSolution5DateTimePartials.java
TestKata6StreamsInDateTime.java	TestSolution6StreamsInDateTime.java

Take Away

The key take-away from this kata is a solid understanding of the Java Time API.