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2. © 2019 | GFT Technologies SE and its affiliates. All rights reserved.
 Od 12 lat w branży IT
 Od 8 miesięcy w GFT Poland
 Programista Java, Kotlin oraz Python
 Pasjonat chmury -
6 certyfikatów z GCP
Krótko o mnie

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Agenda
1. Krótko o Kotinie
2. Podstawy
3. Przydatne ficzery
4. Kotlin i programowanie funkcyjne
5. Jak dodać Kotlin do projektu
6. Aplikacja Spring Boot w Kotlinie vs Java
7. Kotlin w GFT
8. Q&A

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Kotlin?
Kotlin jest językiem programowania ogólnego przeznaczenia, który czyni developerów szczęśliwszym.
Open source na zawsze.
Dobry do:
 Mobile cross-platform
 Server-side
 Native
 Web development
 Data science
 Android

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Krótka historia Kotlina
 2010 - początki prac nad Kotlinem
 02.2012 - Kotlin został otwarty na licencji Apache 2
 02.2016 - Kotlin 1.0 - pierwszy oficjalny release
 05.2017 - Google ogłasza wsparcie Kotlina na Androidzie
 11.2017 - Kotlin 1.2 - wsparcie dla JS
 10.2018 - Kotlin 1.3 - Coroutines - programowanie asynchroniczne
 05.2019 - Google ogłasza Kotlin preferowanym językiem na Androida

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Kto i dlaczego?
Kto?
JetBrains - autorzy IntelliJ, WebStorm, PyCharm
Dlaczego?
“Większośc języków nie ma ficzerów, których szukamy, za wyjątkiem Scali. Scala z kolei kompiluje
się bardzo wolno, dlatego chcemy żeby Kotlin kompilował się równie szybko, co Java.”

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Skąd ta nazwa?
Java
Java
Kotlin

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Java vs Kotlin
Dlaczego Kotlin?
 zwięzła składnia - średnio o 40% mniej linii kodu
 szybciej się w nim pisze
 lepsze wsparcie dla programowania funkcyjnego
 czytelna składnia - mniej boilerplate
 przydatne ficzery - smart cast, extension functions i wiele innych
 brak checked exceptions
 wieloplatformowy - JVM, native, JS, Data Science, Android, multiplatform
 kompatybilny z bibliotekami Javy
 100% współpracuje z Javą

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Basics - variables
 val - immutable variable
 var - mutable variable
 inferred type
 top level variables
 comments

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Basics - functions
 entry point
 functions
 default parameters
 inferred return type
 Unit return type
 function calls
 named parameters
 omit default parameters

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Basics - classes
 constructor
 getters
 setters
 val vs var
 secondary constructor

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Basics - classes inheritance
 Each class inherits from Any
 Any has three methods:
 equals()
 hashCode()
 toString()
 class has to be open
 explicit override
 interfaces
 abstract classes

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Basics - strings and ifs
 String templates
 use variables
 use expressions
 If block
 short syntax
 is an expression

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Basics - objects and properties
 no new keyword
 . access calls getters and setters
 explicit getter and setter
 there is a lot more

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Basics - loops and when
 for loop
 while loop
 when expression
 expression or statement
 multiple cases in one branch
 use expressions
 us is check

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Useful features - smart casting
 is operator
 automatic cast to type
 … in block scope
 … in expression scope

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Useful features - ranges
 check if number in range
 check if number out of range
 iterate over range
 iterate over progression

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Useful features - nullable types
 nullable types
 null checks at compilation
time
 safe calls required for
nullable variables

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Useful features - safe calls and operators
?:
Elvis Operator

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Useful features - filtering out nulls

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Useful features - extension functions
 add function to any class
 even external closed APIs
 we can add functionality to closed classes

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Functional programming
 functions as first class citizens
 use functions as building blocks
 immutable data
 pure functions
 function as a type
 higher order functions
 anonymous functions

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Function as a type

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Lambdas
 used as variables
 no need for explicit type
 call as functions

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Inline functions

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Jest tego o wiele więcej
 delegate properties
 coroutines
 immutable collections
 singletons
 list, dict and set comprehension
 destructuring
 utility function - run(), let(), with()
 data classes
 ...

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Jak dodać Kotlin do projektu?
Add and configure Kotlin Maven Plugin:
Hibernate - https://kotlinexpertise.com/hibernate-with-kotlin-spring-boot/

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Spring Boot loves Kotlin

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Main class
Looks familiar...

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Configuration

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Entities - field definitions

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Entities - constructor

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Entities - getter and setters

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Repository

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Controller - initialisation

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Controller - operations

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Some utilities

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Tests

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GFT & Kotlin
 Wirtualny bank budowany od zera
 ponad 200 deweloperów z całego świata, w tym 50 osób z GFT
 MIkroserwisy 100% napisane w Kotlin ze Spring Boot
 80 mikroserwisów - klaster Kubernetes
 integracja mikroserwisów poprzez REST i Kafkę
 Contract First - OPEN API 3
 DDD i CQRS
 cloud native - AWS
A to tylko jeden z naszych projektów, w którym używamy Kotlina.

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Q&A

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Linki
 Kotlin page: https://kotlinlang.org/
 Try Kotlin: https://try.kotlinlang.org/
 Jetbrains Academy: https://www.jetbrains.com/academy/
 Kotlin for Java Developers: https://www.coursera.org/learn/kotlin-for-java-developers
 Add Kotlin to your project: https://www.baeldung.com/kotlin-maven-java-project