One repo to rule them all. Java code katas - using JUnit5

The java-katas is a code repository for learning various Java features.

From http://wikipedia: Kata originally were teaching and training methods by which successful combat techniques were preserved and passed on. Practicing kata allowed a company of persons to engage in a struggle using a systematic approaches, rather by practicing in a repetitive manner the learner develops the ability to execute those techniques and movements in a natural, reflex-like manner. Systematic practice does not mean permanently rigid. The goal is to internalize the movements and techniques of a kata so they can be executed and adapted under different circumstances, without thought or hesitation. A novice’s actions will look uneven and difficult, while a master’s appear simple and smooth.

From http://codekata.com: Code Kata is an attempt to bring the element of practice to software development. A kata is an exercise in karate where you repeat a form many, many times, making little improvements in each. The intent behind code kata is similar. Each is a short exercise (perhaps 30 minutes to an hour long). Some involve programming, and can be coded in many different ways. Some are open ended, and involve thinking about the issues behind programming. These are unlikely to have a single correct answer.

Code katas were first introduced by Dave Thomas and are an great tool to practice programming something new.

This Git repo is a collection of several code katas about features, utilities and APIs in Java language.

The general structure of each project is a maven quickstart project with a pom.xml, a src directory that contains at least two directories. Code Katas are available under the src/test/java while solutions are under src/solutions/java under each module. The code katas typically contain failing tests with TODO markers that need to be fixed in order to fix the test,

Remember, the src/solutions may not be the perfect way to solve the kata, maybe a solution you come up with is better. Feel free to submit a pull request if you think you have a better solution than the one you find.

1. java-handles: This kata is for understanding Java Reflection and sun.misc.Unsafe usages and also to learn the alternates for those in Method Handles API and VarHandles API in more recent version of Java.
2. java-datetime: This kata is for learning the Java Time API introduced in Java 8, that replaces the java.util.Date and java.util.Calendar with a more humane and extensible API.
3. java-optional: This kata is for learning the Java Optional API, as a replacement for null-checks and unexpected NullPointerExceptions that crop up causing developer unhappiness and/or application instability issues.

More katas will be added, feel free to contribute if you have ideas.