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[JVMLS 12] Kotlin / Java Interop
This document discusses Kotlin and its interoperability with Java. It outlines Kotlin's features like its smart compiler, static typing, and tool support. It then discusses how Kotlin enhances existing Java APIs through extensions and collections interfaces. It also describes Kotlin's approaches to preventing null pointer exceptions through nullable types and annotations. Finally, it examines how Kotlin handles static concepts like packages and class objects that don't exist directly in Kotlin.
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[JVMLS 12] Kotlin / Java Interop
- 1. A Friend InNeed Is a Friend Indeed Kotlin / Java Interop Andrey Breslav Wednesday, August 1, 12 1
- 2. Kotlin Modern Language for Industry • Smart compiler • Static typing ➡ Less boilerplate • Readability • Flexible abstractions • Tool support ➡ Powerful libraries • Interoperability 2 Wednesday, August 1, 12 2
- 3. Stuff • Apache 2 • IDE • Target ➡ IntelliJ ➡ JVM (1.6) ➡ Web Demo ➡ JavaScript * • Build ➡ Ant ➡ Maven 3 * Planned Wednesday, August 1, 12 3
- 4. Outline 4 Wednesday, August 1, 12 4
- 5. Outline • Enhancing Existing APIs ➡ Extensions ➡ Splitting Collections Interfaces 4 Wednesday, August 1, 12 4
- 6. Outline • Enhancing Existing APIs ➡ Extensions ➡ Splitting Collections Interfaces • Fighting for Safety ➡ Nullable types ➡ Interaction with generics 4 Wednesday, August 1, 12 4
- 7. Outline • Enhancing Existing APIs ➡ Extensions ➡ Splitting Collections Interfaces • Fighting for Safety ➡ Nullable types ➡ Interaction with generics • Statics ➡ Packages ➡ Class objects 4 Wednesday, August 1, 12 4
- 8. Making Existing Things Nicer Extensions Variance Tricks Wednesday, August 1, 12 5
- 9. Extensions • Demo 6 Wednesday, August 1, 12 6
- 10. Collections & Variance Java: Kotlin: 7 Wednesday, August 1, 12 7
- 11. Declaration-Site Variance 8 Wednesday, August 1, 12 8
- 12. Translation Ø java.util.List 9 Wednesday, August 1, 12 9
- 13. Translation: Inheritance 10 Wednesday, August 1, 12 10
- 14. Translation: Variance 11 Wednesday, August 1, 12 11
- 15. Calling Java FromKotlin 12 Wednesday, August 1, 12 12
- 16. Summary • Use JDK collections in Kotlin • Extend them with useful operations • Make them variant for Kotlin • At the expense of some unsoundness around the edges 13 Wednesday, August 1, 12 13
- 17. Fighting NPEs Nullable Types Annotating Java Code Wednesday, August 1, 12 14
- 18. Nullable Types • Demo 15 Wednesday, August 1, 12 15
- 19. Nullable Types Summary • null is a legitimate value, not a sin • No overhead (as opposed to Option) • Proper subtyping: ➡ List<String> is a List<String?> • At the expense of: file.getParent()!!.getName()!! 16 Wednesday, August 1, 12 16
- 20. Annotations to TheRescue String String? JSR 305: Annotations for Software Defect Detection 17 Wednesday, August 1, 12 17
- 21. Generics?! @NotNull doesn't help 18 Wednesday, August 1, 12 18
- 22. More Use-Cases of@Kotlin 19 Wednesday, August 1, 12 19
- 23. External Annotations 20 Wednesday, August 1, 12 20
- 24. It Is NotSo Bad • IDE aids annotating with quick fixes • Some annotations can be inferred automatically • Alternative: have a special kind of types for Java things 21 Wednesday, August 1, 12 21
- 25. Statics Packages Class Objects Wednesday, August 1, 12 22
- 26. Package-Level Code file1.kt foo/namespace.class file2.kt 23 Wednesday, August 1, 12 23
- 27. Package-Level Code file1.kt foo/namespace.class Compiled From: file1.kt file2.kt 23 Wednesday, August 1, 12 23
- 28. Package-Level Code file1.kt foo/namespace.class foo/namespace$file1.class from: file1.kt foo/namespace$file2.class file2.kt from: file2.kt 24 Wednesday, August 1, 12 24
- 29. Package-Level Code file1.kt foo/namespace.class foo/namespace$file1.class from: Initialization Order?! file1.kt foo/namespace$file2.class file2.kt from: file2.kt 24 Wednesday, August 1, 12 24
- 30. Kotlin Classes Have No Statics Wednesday, August 1, 12 25
- 31. Class Object Translation 26 Wednesday, August 1, 12 26
- 32. Class Object Translation Only fields! 26 Wednesday, August 1, 12 26
- 33. Resources • Docs: http://kotlin.jetbrains.org • Demo: http://kotlin-demo.jetbrains.com • Code: http://github.com/jetbrains/kotlin • Twitter: ➡ @project_kotlin ➡ @abreslav 27 Wednesday, August 1, 12 27