kotlin-examples

A project that shows Kotlin language features that differ from java (https://kotlinlang.org/)

Table of contents:

• Static Analysis QA Checks
• Project structure
• Building project
• Libraries
• Logging configuration
• Code coverage
• Kotlin features
• Ideas to try

Checks

Jacoco/cobertura code coverage, pmd, checkstyle, enforcer, findbugs

Project structure

Each sub project follows the structure Maven project that consists of the following parts:

• Kotlin main classes are under (src/main/kotlin) with different classes with kotlin features.
• Test extensions for executing tests (src/test/kotlin) that show kotlin features and run during the build

Building project

mvn clean package

Pom.xml

Libraries:

• kotlin

Logging

Standard output is used

Coverage

Coveralls and Cobertura are not good with generated code, so Delegates example with ObservableValue and VarArgExample were excluded from coverage.

Kotlin features

• TopLevelFunction function as first class citizen
• ExtSimpleService example of adding functionality (method) into existing class (problems can occur with separate compilation)
• FactorialTailRec tail recursion example
• NullableNonNullableReturnTypeExample example that shows nullable and notNullable types with ? in the end
• WhenExample potentially more powerful instrument than java switch statement
• Transaction kotlin data POJO example. data notation generates equals and hashcode, costructor generation, val - readonly properties, so only getters will be generated destructing and equality declaration example
• Dollar shows
  • Operator overrides.
  • Operator overloading
  • Equals and hashcode override_operators
  • Try/catch expression values
  • Copy value
  • Referential and structural equals
  • Destructuring object
  • Inlining by locking example // coverage tool does not cover inline functions
  • Infix function
  • Null check do
  • Closure
  • Dollar Range implementation
• DollarProgression progression implementation with internal visibility modifier to be visible inside module
• VarArgExample shows vararg parameters example
• Delegation example of Delegation pattern alternative to Inheritance
• SealedExample feature of closing functionality inside sealed class. Not possible to extend class hierarchy from outside. Plus companion object example, cause there is no static members
• variance examples of Producer/Consumer pattern to make safe casts and assignments
• SpringExampleTest integration with spring framework
• ObservableTest observable feature example (kind of value changed listener)
• Mapping mapping from Map to class fields example
• DeprecatedTest example of kotlin deprecation and tooling of Intellij idea for deprecation

Ideas

• From reference https://kotlinlang.org/docs/reference/
• Kotlin conf 2017 https://www.youtube.com/playlist?list=PLQ176FUIyIUY6UK1cgVsbdPYA3X5WLam5