JDD 2017: Kotlin for Java developers (Tomasz Kleszczyński)
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The document discusses Kotlin, a statically typed programming language designed for multi-platform applications and emphasizing features that Java developers should know. It highlights Kotlin's interoperability with Java, its concise syntax, null safety, and advanced features like extension functions and data classes. Additionally, it outlines the ecosystem, tooling support, and resources for getting started with Kotlin.
![Data classes
● equals() / hashCode() pair
● toString() “Account[email=test]”
● componentN() functions in their order
of declaration
● copy() function](https://image.slidesharecdn.com/kotlinforjavadevelopers-180112071009/85/JDD-2017-Kotlin-for-Java-developers-Tomasz-Kleszczynski-7-320.jpg)
![Operator overloading
● +, -, *, /, %, ..
○ a + b -> a.plus(b)
○ a..b -> a.rangeTo(b)
● in, !in
○ a.contains(b)
● Indexed access []
○ a[i] -> a.get(i)
○ a[i] = b -> a.set(i, b)
● Invoke
○ a(i, j) -> a.invoke(i, j)
● a == b
○ a?.equals(b) ?: (b === null)
● a > b, a < b, a >= b, a <= b -> a.compareTo(b)](https://image.slidesharecdn.com/kotlinforjavadevelopers-180112071009/85/JDD-2017-Kotlin-for-Java-developers-Tomasz-Kleszczynski-11-320.jpg)
JDD 2017: Kotlin for Java developers (Tomasz Kleszczyński)
- 1. Kotlin for Java Developers what every java developer should know about kotlin
- 2. Today I would like to share with you ● Why I care about Kotlin? ● 20 features I love ● 10 features you need to be aware of ● Ecosystem
- 3. Next JVM language? ● Statically typed programming language for multi platform applications ○ concise ○ safe ○ interoperable with Java ○ built together with tooling support ○ open source under Apache 2.0 license ● Version 1.0 released in 2015, current version 1.1.50 (September 2017) ● Google announced first-class support for Kotlin on Android ● Pivotal introduced Kotlin support in Spring Framework 5.0 ● Easy to learn if you know Java
- 6. Extension functions and properties
- 7. Data classes ● equals() / hashCode() pair ● toString() “Account[email=test]” ● componentN() functions in their order of declaration ● copy() function
- 9. Null safety ● Types defines nullability ○ Platform types ● Safe calls ● Elvis operator ● !!. operator ● Safe casts
- 10. when
- 11. Operator overloading ● +, -, *, /, %, .. ○ a + b -> a.plus(b) ○ a..b -> a.rangeTo(b) ● in, !in ○ a.contains(b) ● Indexed access [] ○ a[i] -> a.get(i) ○ a[i] = b -> a.set(i, b) ● Invoke ○ a(i, j) -> a.invoke(i, j) ● a == b ○ a?.equals(b) ?: (b === null) ● a > b, a < b, a >= b, a <= b -> a.compareTo(b)
- 13. Default and named parameters
- 14. Smart casts
- 15. Destructuring objects ● underscore for unused variables (1.1) ● destructuring in lambdas (1.1)
- 17. Expressions and statements ● if and when are expressions, not statements ○ val length = if (a is String) a.length else -1 ○ val action = when (test) { in 0..5 -> OPEN else -> CLOSE } ● assignment is a statement, not an expression ○ if (a = b) does not compile ○ while ((line = bufferedReader.readLine()) != null) does not compile
- 18. Packages and source code structure ● packages ● import allows to import classes, functions, * ● type aliases ● multiple classes in one file ● arbitrary file names ● arbitrary directory structure ● visibility modifiers: private, protected, internal, public
- 19. Other languages have all these features ● Null safety ● No checked exceptions ● Extension functions ● Function types and lambdas ● Default and named parameters ● Properties ● Operator overloading ● Smart casts ● Data classes ● Immutable collections ● Enhanced switch-case ● String templates ● Ranges ● Infix notation ● Inline functions ● Coroutines (async/await) ● Great standard library ● Sealed classes ● Delegated and lazy properties ● Class delegation ● Singletons ● Nested functions ● Object decomposition ● Top-level functions ● Reified generics ● Raw strings ● 100% interoperable with Java 6 ● And more...
- 20. Compile and run with Java code ● you can mix Java and Kotlin code in one project ● experiment with new language without breaking or rewriting the whole application ● small memory footprint of the Kotlin standard library
- 22. What you need to know ● final by default and bytecode generation ● platform types and nullability ● no primitives, no implicit widening conversions for numbers ● standard library
- 23. Final by default and bytecode generation ● all classes, methods are final by default ○ tedious opening via ‘open’ keyword ○ interference with AOP (CGLIB), workarounds as compiler plugins ‘kotlin-spring’, ‘all-open’ ● ‘override’ is a required keyword, not an annotation ● designing for inheritance ● kotlinc generates Java 6 or Java 8 bytecode ● on JVM lambdas does not use ‘invokedynamic’ ● Kotlin Bytecode Generation and Runtime Performance
- 24. Platform types and nullability (!) ● any reference in Java may be null ● types of Java declarations are called platform types ● can be assigned to nullable or non-null type ● compiler, tools refers to them using as T! which means T ot T? ● nullability annotations (JSR-305, Android, Lombok, JetBrains, Eclipse)
- 25. Standard library ● kotlin-runtime and kotlin-stdlib -> kotlin-stdlib ○ < 1MB jar (JVM) ● Kotlin classes and extension functions to Java classes ○ kotlin ○ kotlin.collections ○ kotlin.comparisons ○ kotlin.concurrent ○ kotlin.io ○ kotlin.streams ○ kotlin.text ● kotlin.js
- 27. Platforms and tooling ● JVM a. Java 6 and 8 ● Android ● JavaScript (ES5.1) a. compatible with module systems like AMD, CommonJS ● native (LLVM) a. LLVM is used to compile Kotlin into native code b. technology preview for iOS, linux, MAC, (windows in the work) ● IntelliJ IDEA (Java to Kotlin converter), Eclipse ● Gradle, Maven, Ant
- 28. Where to start? ● Try online https://try.kotlinlang.org/ ● Kotlin is Awesome! https://kotlin.link/
- 29. What will be your next JVM language? https://en.wikipedia.org/wiki/List_of_JVM_languages