JavaCro'14 - Is there Kotlin after Java 8 – Ivan Turčinović and Igor Buzatović
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Kotlin is a statically typed language that compiles to JVM bytecode and JavaScript. While Java 8 introduced improvements like lambdas and default methods, Kotlin is still considered more elegant and concise due to features like null safety, ranges, pattern matching, data classes, extension functions, and type-safe builders. Kotlin also supports operator overloading and collection APIs that are covariant by default.
JavaCro'14 - Is there Kotlin after Java 8 – Ivan Turčinović and Igor Buzatović
- 1. Is there Kotlin after Java 8 Ivan Turčinović & Igor Buzatović
- 2. What is Kotlin?General 2 Statically typed, JVM-targeted language Design principles: Industrial use, tooling, safety Compiles to JVM byte code and JavaScript Runtime size 800K
- 3. Current status, plans, release dateGeneral No release date, no spec yet Roadmap M1 → M2 → … → Beta → Jetbrains project → V1.0 Latest milestone → M7 3 Some frameworks/libraries already appeared Kara Web Framework – Statically typed HTML/CSS Spek – Specification/test framework Kannotator – Infer annotations from bytecode KotlinPrimavera - Kotlin libraries to Spring projects
- 4. Java strikes back with Java 8 Advantages over Java 7 are overwhelming Java 8 introduced Lambdas General 4 Lambdas Null safety (“Optional” class) Default methods Streams API New Date & Time API
- 5. But even with Java 8 Kotlin still... Is more elegant, concise and safe General 5 Has more cool stuff
- 6. Basic syntax and rulesMore elegant? Functions - definition in package or in class Immutable/mutable variables No „new” keyword Type inference 6 Type inference No checked exceptions No primitive types No static members
- 7. More elegant? Basic syntax and rules cont’d 7 Primary constructors No fields, just properties Bean style classes easy to declare By default, all classes are final
- 8. More elegant? Null safety • Null reference – Billion dollar mistake • Kotlin is designed in a way that aims to eliminate NPE from our code 8
- 9. GenericsMore elegant? Not co-variant by default, reason? Wildcards, use-site variance Co-variance price, producers Contra-variance, consumers Bloch: "PECS: Producer extend, Consumer super“ Java 9 Declaration-site variance out / in generics modifiers Supports use-site variance also No wildcard syntax, out / in used Kotlin Java survey: 39% of wildcards usage can be replaced by declaration-site variance
- 10. Default arguments, named argumentsMore cool stuff Default argument values can be defined Arguments with default values are optional No more need for function overloading (almost) 10 overloading (almost) Kotlin classes can have only one constructor Arguments can be called by name When passing arguments by name ordering doesn’t matter
- 11. RangesMore cool stuff Simpler “is it in range” check Can be used for any type that implements Comparable “both ends“ included “..” operator is translated to “rangeTo” function 11 “rangeTo” function “rangeTo” function is implemented as extension function on Comparable Numerical ranges can be iterated over In both directions and in arbitrary steps
- 12. Pattern matchingMore cool stuff Java’s instaceof not very practical No !instanceof Meet Kotlin’s "is“ 12 "is" negation "!is“ Automatic type cast when “is” evaluates true inside if / when blocks
- 13. Data classesMore cool stuff Classes very easy to declare Data annotation changes 13 Output javacro.User@41a7d9e7 1101519335 1926426205 false Data annotation changes behavior of hashCode, equals, toString functions Default implementation uses all properties Off course we can override
- 14. Data classesMore cool stuff Classes very easy to declare Data annotation changes 14 Output User(firstName=John,lastName=Doe) 71819599 71819599 true Data annotation changes behavior of hashCode, equals, toString functions Default implementation uses all properties Off course we can override
- 15. Operator overloadingMore cool stuff Operators are translated to corresponding functions Operator set is fixed Operator overloading is achieved by overriding corresponding functions of specific class 15 specific class By adding extension functions we can enable certain operator for classes that don’t support it originally On our own classes we can enable certain operator by implementing corresponding functions
- 16. Extension functionsMore cool stuff What to do if we want to add features to existing classes Java: extending or utility classes Kotlin: add functions to existing classes without changing their code Example: implement BigDecimal + 16 Example: implement BigDecimal + operator How does it work “behind the scene”?
- 17. Extension functionsMore cool stuff What to do if we want to add features to existing classes Java: extending or utility classes Kotlin: add functions to existing classes without changing their code Example: implement BigDecimal + 17 Example: implement BigDecimal + operator How does it work “behind the scene”?
- 18. Kotlin collectionsMore cool stuff 18 Read-only traits on top, co-variant Extended by mutable traits Implemented by JDK classes (compile time modifications) Read-only traits do not guarantee immutability Top level package functions for instantiating collections: Read-only: setOf, listOf, mapOf Mutable: hashSetOff, arrayListOf, hashMapOf
- 19. Type-safe Groovy-style buildersMore cool stuff 19 For generating tree-like structures (UI layouts, 3D scene graphs) Tree-like syntax – better insight in what is being generated Functions create, initialize and return builder specific objects Better then xml: no scheme required, type safe, interoperable with other code
- 20. Type-safe Groovy-style buildersMore cool stuff Objects initialized using function literal argument Extension function literal allows referencing to object enclosing element 20 enclosing element Kara web framework using it for HTML layouts, CSS Android apps, XML layouts