Java vs Kotlin

Introduction of Kotlin for Java developers with side by side comparison

Transcript

1. Java vs Kotlin Danny Preussler Kotlin everywhere
2. about:me •Java developer since 2003 •Kotlin developer since 2016 •Google Developer Expert for Android and Kotlin •Introduced Kotlin at Groupon and Viacom
5. Kotlin adoption •Languages developers want to learn in 2019 • https://research.hackerrank.com/ developer-skills/2019
6. Kotlin adoption Okt 18, GitHub: 'Kotlin for Android now fastest-growing programming language' https://www.zdnet.com/article/microsofts-github-kotlin-for-android-no w-fastest-growing-programming-language/
7. Kotlin adoption Stackoverflow trends of JVM languages. #kotlin is first with a strong growth during the last 2 years.
8. Kotlin adoption • JVM Ecosystem Report 2018 (10k questionaires): What is the principal JVM language you use for your main applications? • Kotlin edges past Groovy and Scala in language usage on 2.42% https://snyk.io/blog/jvm-ecosystem-report-2018/
9. Kotlin adoption •1.5M+ developers edited Kotlin code in 2018 •100M+ lines of Kotlin code •96,000+ Kotlin GitHub repositories •Android — 1 in 4 apps (from top 1000) uses Kotlin •Server — х2 from 2017 https://www.jetbrains.com/annualreport/2018/community/
10. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 The year: 2010 Java6 has been around the 4th year
11. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 The year: 2010 Kotlin Development started internally
12. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 July 2010 Swift Development started
13. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 July 2011 Java 7
14. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 July 2011 JetBrains unveiled Project Kotlin
15. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 February 2012 JetBrains open sourced Kotlin
16. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 March 2014 Java 8
17. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 June 2014 WWDC application became the first publicly released Swift app
18. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 September 2014 Swift 1.0
19. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 Februar 2016 Kotlin 1.0
20. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 Google I/O 2017 Official Kotlin support for Android
21. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 September 2017 Java 9
22. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 March 2018 Java 10
23. 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 Google I/O 2019 Kotlin becomes preferred language for Android
24. Why Kotlin?
25. Goals of Kotlin Modern language Faster compilation than Scala Smaller footprint than Scala Designed to work perfectly with Java (designed for 6+8)
26. Why Kotlin? Null safe Functional aspects Strongly typed but type Inference Reduces boilerplate
27. Kotlin is.. Strongly typed Dynamic typed Object orientated Functional kotlin java scala groovy clojure
28. Makes developers happy Happiness
29. Basics String someString; final String someConstantString;
30. Basics
31. Basics var someString: String val someConstantString: String
32. The power of type inference Integer doSomething(String someString) { return someString.getLength(); }
33. The power of type inference
34. The power of type inference fun doSomething(someString: String): Int { return someString.length }
35. The power of type inference fun doSomething(someString: String): Int = someString.length
36. The power of type inference fun doSomething(someString: String) = someString.length
37. Type inference in Java HashMap<String,Integer> x = new HashMap<String,Integer>();
38. Type inference in Java HashMap<String,Integer> x = new HashMap();
39. Type inference in Java 10 var x = new HashMap<String,Integer>();
40. Type inference in Java 10 Difference to Kotlin: • var is not a keyword in Java 10 • it‘s a reserved type name
41. Let’s talk about null
42. Lets talk null I call it my billion-dollar mistake. It was the invention of the null reference in 1965   Tony Hoare ( inventor of the null reference)
43. Lets talk null if (button != null){ button.onPressed(); }
44. Lets talk null if (button.isPresent()){ button.get().onPressed(); }
45. Lets talk null
46. Lets talk null button?.onPressed()
47. Lets talk null someString?.length
48. Lets talk null someString?.length ?: 0
49. Lets talk null someString!!.length
50. Lets talk null val someString : String? …
51. Lets talk null •Equivalent in Java: @NonNull but runtime crash vs compiler only •Nullability is Part of Typesystem
52. Lets talk null fun some(thing: String?) {…} public final void some( @Nullable String thing) {…}
53. Lets talk null fun some(thing: String) {…} public final void some( @NotNull String thing) { checkParameterIsNotNull(thing, "thing"); }
54. Smart casts Object someString … if (someString instanceOf String) { ((String)someString).getLength(); }
55. Smart casts
56. Smart casts val someString : Any if (someString is String) { someString.length }
57. Getter, setter view.setVisibility(View.GONE);
58. Getter, setter
59. Getter, setter view.visibility = View.GONE
60. Lambdas •Came in Java-8 •Android devs had to rely on Retrolambda very long
61. Lambdas list.forEach( element -> System.out.println(element) );
62. Lambdas
63. Lambdas list.forEach{ element -> System.out.println(element) }
64. Lambdas list.forEach{ System.out.println(it) }
65. Collections List<String> myList = Arrays.asList("1", "2", "3")
66. Collections
67. Collections val myList = listOf("1", "2", "3") val myList = mutablelistOf("1", "2", "3")
68. Streams tags.stream() .map(tag -> tag.replace("#", "")) .collect(joining(",");
69. Streams
70. Streams tags.map{ it.replace("#", "") } .join(",")
71. Streams tags.asSequence(). .map{ it.replace("#", "") } .join(",")
72. default parameters vs overloading class Api { Api(String baseURl) { this(baseURl, CacheStrategy.NO_CACHE) } Api(String baseURl, CacheStrategy cache) { } }
73. default parameters vs overloading
74. default parameters vs overloading class Api( baseUrl: String, cache: CacheStrategy = CacheStrategy.NO_CACHE )
75. default parameters vs overloading class Api( private val baseUrl: String, val cache: CacheStrategy = CacheStrategy.NO_CACHE )
76. Data classes data class Team( val name: String? = null, val logo: String? = null )
77. Sealed classes sealed class LoadingState { class Loading : LoadingState() class Loaded : LoadingState() class Empty : LoadingState() }
78. Lazy initialization public class LazyField { private String value; public String getValue() { if (value == null) { value = computeValue(); } return value } private String computeValue() { .... } }
79. Lazy initialization
80. Lazy initialization class LazyField { val: String by lazy { computeValue() } private fun computeValue()= … }
81. Lazy initialization •Framework class like Activities: no control over constructor •How use the compiler to check for null?
82. Late initialization •Framework class like Activities: no control over constructor •How use the compiler to check for null?
83. Late initialization View someView; ... someView = findViewbyId(R.id.myView);
84. Late initialization
85. Late initialization lateinit someView: View ... someView = findViewbyId(R.id.myView);
86. Primitives in Kotlin
87. Primitives in Kotlin •No primitives
88. Primitives in Kotlin •No primitives int a; Integer b; a: Int
89. Primitives in Kotlin •No primitives •Boxing? Therefore no boxing issues (mostly) int a; Integer b; a: Int
90. Primitives in Kotlin: Costs? •The numeric type usages in Kotlin are compiled into JVM primitives where possible. •Compiler decides
91. Primitives in Kotlin: Costs? •The numeric type usages in Kotlin are compiled into JVM primitives where possible. •Compiler decides •Works because of missing widening int a = 1; double b = a; val a:Int = 1 val b:Double = a
92. Primitives in Kotlin •Nullable type cannot be primitive •Primitives cannot be used as a generic type argument. •List<Int> is equivalent of Java List<Integer> •Therefore IntArray as type!
93. Operator overloading
94. Operator overloading operator fun plusAssign(callback: Callback) { callbacks.add(callback) } operator fun minusAssign(callback: Callback) { callbacks.remove(callback) } adapterCallbacks += {…}
95. Expression Translated to a++ a.inc() + see below a-- a.dec() + see below Expression Translated to +a a.unaryPlus() -a a.unaryMinus() !a a.not() Expression Translated to a + b a.plus(b) a - b a.minus(b) a * b a.times(b) a / b a.div(b) a % b a.rem(b), a.mod(b) (deprecated) a..b a.rangeTo(b)
96. Operator overloading Expression Translated to a > b a.compareTo(b) > 0 a < b a.compareTo(b) < 0 a >= b a.compareTo(b) >= 0 a <= b a.compareTo(b) <= 0 Expression Translated to a == b a?.equals(b) ?: (b === null) a != b !(a?.equals(b) ?: (b === null))
97. Operator overloading Expression Translated to a in b b.contains(a) a !in b !b.contains(a) Expression Translated to a[i] a.get(i) a[i, j] a.get(i, j) a[i_1, ..., i_n] a.get(i_1, ..., i_n) a[i] = b a.set(i, b) a[i, j] = b a.set(i, j, b) a[i_1, ..., i_n] = b a.set(i_1, ..., i_n, b)
98. Operator overloading Expression Translated to a() a.invoke() a(i) a.invoke(i) a(i, j) a.invoke(i, j) a(i_1, ..., i_n) a.invoke(i_1, ..., i_n) Expression Translated to a += b a.plusAssign(b) a -= b a.minusAssign(b) a *= b a.timesAssign(b) a /= b a.divAssign(b) a %= b a.remAssign(b), a.modAssign(b) (deprecated)
99. Operator overloading •Range expression for (i in 1..4) print(i) operator fun rangeTo(other: Int) = IntRange(this, other)
100. Operator overloading in RxKotlin disposables += clips.subscribeBy( onError = { logE(it) }, onNext = { onNewClip(it) } )
101. Getter / Setter var live = true private set
102. Getter / Setter val live get() = category.live val live = category.live
103. Getter / Setter val live get() = category.live
104. Getter / Setter val live get() = category.live public final boolean getLive() { return category.getLive(); }
105. Delegated properties var something: Something by lazy{} var something: Something by inject{}
106. Delegation •inheritance Effective Java: Item 16: Favor composition over inheritance class FirebaseFeatureFlags ( private val defaults: DefaultFeatureFlags ) : FeatureFlags by defaults {
107. Singleton class Singleton { final static Singleton instance = new Singleton() private Singleton() {} }
108. Singleton
109. Singleton object Singleton
110. Extension functions class Utils { public static boolean isNonNullOrEmpty(String string){ … } } isNonNullOrEmpty(“hallo“)
111. Extension functions
112. Extension functions fun String?.isNonNullOrEmpty() = {…} “hallo“.isNonNullOrEmpty()
113. Extension functions fun String?.isNonNullOrEmpty() = {…} public static final boolean isNonNullOrEmpty( @Nullable String $receiver) {… }
114. Standard functions val calendar = Calendar.getInstance(Locale.US).apply { set(Calendar.DAY_OF_MONTH, 3) set(Calendar.MONTH, Calendar.MARCH) set(Calendar.YEAR, 1990) }
115. Standard functions
116. Infix val game = homeTeam.vs(guestTeam)
117. Infix val game = homeTeam.vs(guestTeam) val game = homeTeam vs guestTeam
118. Infix val game = homeTeam.vs(guestTeam) val game = homeTeam vs guestTeam infix fun Team.vs(team: Team) = Pairing(this, team)
119. @Test void shouldMapComponentsToDomain()
120. @Test void should_map_components_to_domain()
122. @Test void `should map components to domain`()
123. inlining
124. inline •Avoid runtime penalties of wrappers by inline”ing
125. inline •Powerful with reified: Allows generics with type check: T::class inline fun <reified T : Context> Activity.start() { startActivity(Intent(this, T::class.java)) }
126. inline inline fun <reified T : Context> Activity.start() { startActivity(Intent(this, T::class.java)) } start<MainActivity>() $receiver$iv.startActivity( new Intent( (Context)$receiver$iv, MainActivity.class) );
127. inline •Inline classes •Experimental inline class Time(private val timeMs: Long)
128. inline •Inline classes •Experimental •Inline classes are final •Can lead to weird boxing issues •Not compatible with @Parcelize inline class Time(private val timeMs: Long)
129. Coroutines
130. • Lightweight threads • Allows asynchronous code to be written sequentially suspend fun concurrentSum(): Int = coroutineScope { val one = async { doSomethingUsefulOne() } val two = async { doSomethingUsefulTwo() } one.await() + two.await() }
131. Some changes
132. In/out https://twitter.com/fmuntenescu/status/982268265853476867
133. Static? class Job { static String ERROR = null }
134. Static? class Job { companion object { var ERROR: String = null } }
135. Other changes •Classes/methods public by default
136. Other changes •Classes/methods public by default •Classes/methods final by default (vs open)
137. Other changes •Classes/methods public by default •Classes/methods final by default (vs open) •Inner class: static by default (vs inner)
138. Other changes •Classes/methods public by default •Classes/methods final by default (vs open) •Inner class: static by default (vs inner) •Stricter usage of protected
139. Other changes •Classes/methods public by default •Classes/methods final by default (vs open) •Inner class: static by default (vs inner) •Stricter usage of protected •New visibility: internal
140. Other changes •Classes/methods public by default •Classes/methods final by default (vs open) •Inner class: static by default (vs inner) •Stricter usage of protected •New visibility: internal •One file can have multiple public classes
141. Other changes •Classes/methods public by default •Classes/methods final by default (vs open) •Inner class: static by default (vs inner) •Stricter usage of protected •New visibility: internal •One file can have multiple public classes •„global“ functions & variables are allowed
142. Other changes •Classes/methods public by default •Classes/methods final by default (vs open) •Inner class: static by default (vs inner) •Stricter usage of protected •New visibility: internal •One file can have multiple public classes •„global“ functions & variables are allowed •No checked Exceptions
143. Other changes •void -> Unit •Object -> Any
144. Other changes •void -> Unit •Object -> Any •Plus Nothing
145. Bad news something ? 1 : 0 something != null ? something : "" ☹
146. Bad news if (something ) 1 else 0 ☹ something ?: ""
147. Java Interop
148. Java Interop public final class FileKt { public static final void foobar() {..} } //File.kt fun foobar(){..}
149. Java Interop •@JvmOverloads •@JvmStatic •@JvmField •@JvmName •@Throws
150. Java Interop •Careful with „sneaky“ Kotlin exceptions •@Throws
151. Java Interop @Metadata( mv = {1, 1, 13}, bv = {1, 0, 3}, k = 1, d1 = {"\u0000\u0014\n\u0002\u0018\u0002\n\u0002\u0010\ u0000\n\u0002\b\u0002\n\u0002\u0010\u0002\n\u0002 \b\u0003\u0018\u00002\u00020\u0001:\u0001\u0006B\ u0005¢ \u0006\u0002\u0010\u0002J\b\u0010\u0003\u001a\u00 020\u0004H\u0007J\u0006\u0010\u0005\u001a\u00020\ u0004¨\u0006\u0007"}, d2 = {"Lde/jodamob/android/kotlin/T_TestingTest;", "", "()V", "test", "", "throwSomething", "Something", "app"} )
152. Java Interop •Performance in most case same as Java https://de.slideshare.net/intelliyole/kotlin-bytecode-generation-and-runtime-performance
153. Compile time
154. Compile time
155. Runtime • Execution time: difference [..] can vary from 6.7% in favor of Java [..], to 1.2% in favor of Kotlin [..] • Memory consumption: appeared the lowest in the Java implementation in four out of six benchmarks. • CPU load: no significant distinction in load management https://medium.com/@bards95/comparative-evaluation-of-selected-constru cts-in-java-and-kotlin-part-1-dynamic-metrics-2592820ce80
156. Runtime • Execution time: difference [..] can vary from 6.7% in favor of Java [..], to 1.2% in favor of Kotlin [..] • Memory consumption: appeared the lowest in the Java implementation in four out of six benchmarks. • CPU load: no significant distinction in load management https://medium.com/@bards95/comparative-evaluation-of-selected-constru cts-in-java-and-kotlin-part-1-dynamic-metrics-2592820ce80
157. Runtime • Execution time: difference [..] can vary from 6.7% in favor of Java [..], to 1.2% in favor of Kotlin [..] • Memory consumption: appeared the lowest in the Java implementation in four out of six benchmarks. • CPU load: no significant distinction in load management https://medium.com/@bards95/comparative-evaluation-of-selected-constru cts-in-java-and-kotlin-part-1-dynamic-metrics-2592820ce80
158. Sum up
159. Kotlin Less code
160. Less Code Kotlin .. helps to increase a cut in the lines of code by approximately 40 % (JetBrains) … tests show … the number of code lines reduces by 30… https://belitsoft.com/apps-development-services/java-vs-kotlin
161. Kotlin Less code No more null
162. Kotlin Less code Easy to learn No more null
163. Kotlin No revolution
164. Kotlin No revolution Just evolution
165. Kotlin No revolution (pragmatic) evolution
166. Kotlin ‘Kotlin isn't revolutionary (with the possible exception of its null-handling) but feels like a very careful amalgamation of some of the best features of other languages. Rob Fletcher, Netflix https://belitsoft.com/apps-development-services/java-vs-kotlin
167. Kotlin is … „Scala for Dummies” https://towardsdatascience.com/introduction-to-kotlin-statistics-cdad3be88b5
168. Makes developers happy fun fun fun
169. Get started
170. Thank you @PreusslerBerlin