Kotlin: New Hope in a Java 6 Wasteland

Java 8 was released last year adding lambdas, streams, and many other language improvements. Java 9 is already in the works, but with over half of Android devices stuck using Java 6 will we ever get to use a modern language?

Introducing Kotlin: a statically typed JVM language backed by JetBrains. With features like lambdas, class extensions, and null-safety, it aims to be concise, expressive, and highly interoperable. In this presentation we will learn how powerful Kotlin can be when added to your Android tool belt.

Transcript

1. kotlin: NewHope In a Java 6 Wasteland
2. 100% interoperable with Java™ Statically typed programming language targeting the JVM and JavaScript
3. concise /kənˈsīs/ adjective giving a lot of information clearly and in a few words; brief but comprehensive.
4. expressive /ikˈspresiv/ adjective effectively conveying thought or feeling.
5. safe /sāf/ adjective protected from or not exposed to danger or risk; not likely to be harmed or lost.
6. versatile /ˈvərsədl/ adjective able to adapt or be adapted to many different functions or activities.
7. interoperable /ˌin(t)ərˈäp(ə)rəb(ə)l/ adjective (of computer systems or software) able to exchange and make use of information.
8. Why not wait for Java 8?
9. Java 6 2006
10. Java 6 2006 Android 1.0 2008
11. Java 6 2006 Java 7 2011 Android 1.0 2008
12. Java 6 2006 Java 7 2011 Java 7 Support 2013 Android 1.0 2008
13. Java 6 2006 Java 7 2011 Java 8 2014 Java 7 Support 2013 Android 1.0 2008
14. Java 6 2006 Java 7 2011 Java 8 2014 Java 7 Support 2013 Java 8 Support ???? Android 1.0 2008
15. KitKat Jelly Bean Lollipop Froyo Gingerbread Ice Cream Sandwich
16. KitKat Jelly Bean Lollipop Froyo Gingerbread Ice Cream Sandwich
17. Problems with Java
18. Null references “I call it my billion-dollar mistake… [which] has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.” — Tony Hoare
19. Raw types List numbers = getNumberList(); int sum = 0; for (Object num : numbers) { sum += (Integer) num; // Unchecked cast }
20. Covariant arrays String[] strings = { "hello" }; Object[] objects = strings; objects[0] = 1; // java.lang.ArrayStoreException
21. SAM types interface Func1<T1, R> { R call(T1 t1); } interface Func2<T1, T2, R> { R call(T1 t1, T2 t2); } interface Func3<T1, T2, T3, R> { R call(T1 t1, T2 t2, T3 t3); } // ...
22. Wildcards “I am completely and totally humbled. Laid low. I realize now that I am simply not smart at all. I made the mistake of thinking that I could understand generics. I simply cannot. I just can't. This is really depressing. It is the first time that I've ever not been able to understand something related to computers, in any domain, anywhere, period.” "We simply cannot afford another wildcards” — Joshua Bloch
23. Checked exceptions “… requiring exception specifications could both enhance developer productivity and enhance code quality, but experience with large software projects suggests a different result – decreased productivity and little or no increase in code quality.” — Bruce Eckel
24. Kotlin to the rescue!
25. What Kotlin removes • Checked exceptions • Non-class primitive types • Static members • Non-private fields • Wildcard types
26. What Kotlin adds • Lambdas • Data classes • Function literals & inline functions • Extension functions • Null-safety • Smart casts • String templates • Properties • Primary constructors • Class delegation • Type inference • Singletons • Declaration-site variance • Range expressions
27. Dalvik ART Android Java source javac Kotlin source kotlinc bytecode JVM Backend JVM Desktop
28. Hello, Kotlin!
29. fun main(args: Array<String>): Unit { println("Hello, World!") } > Hello, World!
30. fun main(args: Array<String>): Unit { println("Hello, World!") } Function keyword
31. fun main(args: Array<String>): Unit { println("Hello, World!") } Function name
32. fun main(args: Array<String>): Unit { println("Hello, World!") } Argument name
33. fun main(args: Array<String>): Unit { println("Hello, World!") } Argument type
34. fun main(args: Array<String>): Unit { println("Hello, World!") } Return type
35. fun main(args: Array<String>): Unit { println("Hello, World!") }
36. fun main(args: Array<String>): Unit {. println("Hello, World!") }. Unit inferred
37. fun main(args: Array<String>) {. println("Hello, World!") }.
38. fun main(args: Array<String>) {. println("Hello, World!") }.
39. fun main(args: Array<String>) {. var name = "World" println("Hello, $name!") }.
40. fun main(args: Array<String>) {. var name = "World" println("Hello, $name!") }. Variable declaration
41. fun main(args: Array<String>) {. var name = "World" println("Hello, $name!") }. String interpolation
42. fun main(args: Array<String>) {. var name = "World" if (args.isNotEmpty()) { name = args[0] } println("Hello, $name!") }.
43. fun main(args: Array<String>) {. var name = "World" if (args.isNotEmpty()) { name = args[0] } println("Hello, $name!") }.
44. fun main(args: Array<String>) {. val name = "World" if (args.isNotEmpty()) { name = args[0] } println("Hello, $name!") }.
45. fun main(args: Array<String>) {. val name = "World" if (args.isNotEmpty()) { name = args[0] } println("Hello, $name!") }. Constant declaration
46. fun main(args: Array<String>) {. val name = "World" if (args.isNotEmpty()) { name = args[0] }. println("Hello, $name!") }. Val cannot be reassigned
47. fun main(args: Array<String>) {. val name = "World" if (args.isNotEmpty()) { name = args[0] }. println("Hello, $name!") }.
48. fun main(args: Array<String>) {. val name = if (args.isNotEmpty()) { args[0] } else { "World" }. println("Hello, $name!") }.
49. fun main(args: Array<String>) {. val name = if (args.isNotEmpty()) { args[0] } else { "World" }. println("Hello, $name!") }.
50. fun main(args: Array<String>) {. val name = if (args.isNotEmpty()) { args[0] } else { "World" }. println("Hello, $name!") }. Conditional assignment block
51. fun main(args: Array<String>) { val name = if (args.isNotEmpty()) { args[0] } else { "World" }. println("Hello, $name!") }.
52. fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") }.
53. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") }.
54. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") } Class keyword
55. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") } Class name
56. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") } Primary constructor
57. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") } Non-final class member
58. class Person(var name: String) fun main(args: Array<String>) { val name = if (args.isNotEmpty()) args[0] else "World" println("Hello, $name!") }
59. class Person(var name: String) fun main(args: Array<String>) { println("Hello, $name!") }
60. class Person(var name: String) fun main(args: Array<String>) { val person = Person("Michael") println("Hello, $name!") }
61. class Person(var name: String) fun main(args: Array<String>) { val person = Person("Michael") println("Hello, $name!") }. Instance declaration
62. class Person(var name: String) fun main(args: Array<String>) { val person = Person("Michael") println("Hello, $name!") }.
63. class Person(var name: String) fun main(args: Array<String>) { val person = Person("Michael") println("Hello, ${person.name}!") }. > Hello, Michael!
64. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") } class Person(var name: String) fun main(args: Array<String>) { val person = Person("Michael") println("Hello, ${person.name}!") }.
65. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }.. class Person(var name: String). fun main(args: Array<String>) { val person = Person("Michael") println("Hello, ${person.name}!") }.
66. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }.. class Person(var name: String, var lang: Language). fun main(args: Array<String>) { val person = Person("Michael") println("Hello, ${person.name}!") }.
67. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }.. class Person(var name: String, var lang: Language = Language.EN). fun main(args: Array<String>) { val person = Person("Michael") println("Hello, ${person.name}!") }. Default value
68. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) fun main(args: Array<String>) { val person = Person("Michael") println("Hello, ${person.name}!") }..
69. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }. fun main(args: Array<String>) { val person = Person("Michael") println("Hello, ${person.name}!") }..
70. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") } class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") } fun main(args: Array<String>) { val person = Person("Michael") println("Hello, ${person.name}!") }
71. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") } class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") } fun main(args: Array<String>) { val person = Person("Michael") }
72. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") } class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") } fun main(args: Array<String>) { val person = Person("Michael") person.greet() } > Hello, Michael!
73. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { }.
74. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { val people = listOf( Person("Michael"), Person("Miguel", Language.SP), Person("Michelle", Language.FR) ). }.
75. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { val people = listOf( Person("Michael"), Person("Miguel", Language.SP), Person("Michelle", Language.FR) ). for (person in people) {. person.greet() }. }.
76. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { val people = listOf( Person("Michael"), Person("Miguel", Language.SP), Person("Michelle", Language.FR) ). people.forEach {.person -> person.greet() }. }.
77. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { val people = listOf( Person("Michael"), Person("Miguel", Language.SP), Person("Michelle", Language.FR) ). people.forEach { it.greet() }. }.
78. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { listOf( Person("Michael"), Person("Miguel", Language.SP), Person("Michelle", Language.FR) ).forEach { it.greet() }. }. > Hello, Michael! > Hola, Miguel! > Bonjour, Michelle!
79. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... open class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. fun main(args: Array<String>) { listOf( Person("Michael"), Person("Miguel", Language.SP), Person("Michelle", Language.FR) ).forEach { it.greet() }. }. Non-final
80. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... open class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. class Hispanophone(name: String) : Person(name, Language.ES) class Francophone(name: String) : Person(name, Language.FR) fun main(args: Array<String>) { listOf( Person("Michael"), Person("Miguel", Language.SP), Person("Michelle", Language.FR) ).forEach { it.greet() } }.
81. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... open class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. class Hispanophone(name: String) : Person(name, Language.ES) class Francophone(name: String) : Person(name, Language.FR) fun main(args: Array<String>) { listOf( Person("Michael"), Hispanophone("Miguel"), Francophone("Michelle") ).forEach { it.greet() } }.
82. enum class Language(val greeting: String) { EN("Hello"), ES("Hola"), FR("Bonjour") }... open class Person(var name: String, var lang: Language = Language.EN) { fun greet() = println("${lang.greeting}, $name!") }.. class Hispanophone(name: String) : Person(name, Language.ES) class Francophone(name: String) : Person(name, Language.FR) fun main(args: Array<String>) { listOf( Person("Michael"), Hispanophone("Miguel"), Francophone("Michelle") ).forEach { it.greet() } }.
83. What Kotlin Adds to Java
84. Type inference
85. Type inference String string = "";
86. Type inference var string: String = ""
87. Type inference var string = ""
88. Type inference var string = "" var char = ' '
89. Type inference var string = "" var char = ' ‘ var int = 0
90. Type inference var string = "" var char = ' ‘ var int = 0 var long = 0L
91. Type inference var string = "" var char = ' ‘ var int = 0 var long = 0L var float = 0F
92. Type inference var string = "" var char = ' ‘ var int = 0 var long = 0L var float = 0F var double = 0.0
93. Type inference var string = "" var char = ' ' var int = 0 var long = 0L var float = 0F var double = 0.0 var boolean = true
94. Type inference var string = "" var char = ' ' var int = 0 var long = 0L var float = 0F var double = 0.0 var boolean = true var foo = MyFooType()
95. Null-safety
96. Null-safety String a = null;
97. Null-safety String a = null; System.out.println(a.length());
98. Null-safety String a = null; System.out.println(a.length()); NullPointerException
99. Null-safety val a: String = null
100. Null-safety val a: String = null Non-null type
101. Null-safety val a: String? = null
102. Null-safety val a: String? = null
103. Null-safety val a: String? = null println(a.length())
104. Null-safety val a: String? = null println(a.length()) Unsafe call
105. Null-safety val a: String? = null println(a?.length())
106. Null-safety val a: String? = null println(a?.length()) > null
107. Null-safety int length = a != null ? a.length() : -1
108. Null-safety int length = a != null ? a.length() : -1 Null check
109. Null-safety int length = a != null ? a.length() : -1 Assignment selector
110. Null-safety var length = if (a != null) a.length() else -1
111. Null-safety var length = if (a != null) a.length() else -1 Null check
112. Null-safety var length = if (a != null) a.length() else -1 Assignment selector
113. Null-safety var length = a?.length() ?: -1
114. Null-safety var length = a?.length() ?: -1 Null check
115. Null-safety var length = a?.length() ?: -1 Assignment selector
116. Smart casts
117. Smart casts if (x is String) { print(x.length()) }
118. Smart casts if (x is String) { print(x.length()) } Type check
119. Smart casts if (x is String) { print(x.length()) } Smart cast
120. Smart casts if (x !is String) { return } print(x.size())
121. Smart casts if (x !is String) { return } print(x.size()) Type check
122. Smart casts if (x !is String) { return } print(x.size())
123. Smart casts if (x !is String) { return } print(x.size()) Smart cast
124. Smart casts if (x !is String || x.size() == 0) { return }
125. Smart casts if (x !is String || x.size() == 0) { return } Type check
126. Smart casts if (x !is String || x.size() == 0) { return }
127. Smart casts if (x !is String || x.size() == 0) { return } Smart cast
128. Smart casts if (x is String && x.size() > 0) { print(x.size()) }
129. Smart casts if (x is String && x.size() > 0) { print(x.size()) } Type check
130. Smart casts if (x is String && x.size() > 0) { print(x.size()) }
131. Smart casts if (x is String && x.size() > 0) { print(x.size()) } Smart cast
132. Smart casts if (x is String && x.size() > 0) { print(x.size()) } Smart cast
133. Smart casts when (x) { is Int -> print(x + 1) is String -> print(x.size() + 1) is Array<Int> -> print(x.sum()) }
134. Smart casts when (x) { is Int -> print(x + 1) is String -> print(x.size() + 1) is Array<Int> -> print(x.sum()) } Type check
135. Smart casts when (x) { is Int -> print(x + 1) is String -> print(x.size() + 1) is Array<Int> -> print(x.sum()) } Smart cast
136. Smart casts when (x) { is Int -> print(x + 1) is String -> print(x.size() + 1) is Array<Int> -> print(x.sum()) } Type check
137. Smart casts when (x) { is Int -> print(x + 1) is String -> print(x.size() + 1) is Array<Int> -> print(x.sum()) } Smart cast
138. Smart casts when (x) { is Int -> print(x + 1) is String -> print(x.size() + 1) is Array<Int> -> print(x.sum()) } Type check
139. Smart casts when (x) { is Int -> print(x + 1) is String -> print(x.size() + 1) is Array<Int> -> print(x.sum()) } Smart cast
140. String templates
141. String templates val apples = 4 println("I have " + apples + " apples.") > I have 4 apples.
142. String templates val apples = 4 println("I have $apples apples.") > I have 4 apples. > I have 4 apples.
143. String templates val apples = 4 val bananas = 3 println("I have $apples apples and " + (apples + bananas) + " fruits.") > I have 4 apples. > I have 4 apples. > I have 4 apples and 7 fruits.
144. String templates val apples = 4 val bananas = 3 println("I have $apples apples and ${apples+bananas} fruits.") > I have 4 apples. > I have 4 apples and 7 fruits. > I have 4 apples and 7 fruits.
145. Range expressions
146. Range expressions if (1 <= i && i <= 10) { println(i) }
147. Range expressions if (1 <= i && i <= 10) { println(i) }. if (IntRange(1, 10).contains(i)) { println(i) }.
148. Range expressions if (1 <= i && i <= 10) { println(i) }. if (1.rangeTo(10).contains(i)) { println(i) }.
149. Range expressions if (1 <= i && i <= 10) { println(i) }. if (i in 1..10) { println(i) }. Range operator
150. Range expressions for (i in 1..4) { print(i) }. > 1234
151. Range expressions for (i in 1..4 step 2) { print(i) }. > 1234 > 13
152. Range expressions for (i in 4 downTo 1 step 2) { print(i) }. > 1234 > 13 > 42
153. Range expressions for (i in 1.0..2.0) { print("$i ") }. > 13 > 42 > 1.0 2.0
154. Range expressions for (i in 1.0..2.0 step 0.3) { print("$i ") }. > 42 > 1.0 2.0 > 1.0 1.3 1.6 1.9
155. Higher-order functions & lambdas
156. Higher-order functions & lambdas public interface Function<T, R> { R call(T t); }
157. Higher-order functions & lambdas public interface Function<T, R> { R call(T t); } public static <T> List<T> filter(Collection<T> items, Function<T, Boolean> f) { final List<T> filtered = new ArrayList<T>(); for (T item : items) if (f.call(item)) filtered.add(item); return filtered; }
158. Higher-order functions & lambdas public interface Function<T, R> { R call(T t); } public static <T> List<T> filter(Collection<T> items, Function<T, Boolean> f) { final List<T> filtered = new ArrayList<T>(); for (T item : items) if (f.call(item)) filtered.add(item); return filtered; } filter(numbers, new Function<Integer, Boolean>() { @Override public Boolean call(Integer value) { return value % 2 == 0; } });
159. Higher-order functions & lambdas public interface Function<T, R> { R call(T t); } public static <T> List<T> filter(Collection<T> items, Function<T, Boolean> f) { final List<T> filtered = new ArrayList<T>(); for (T item : items) if (f.call(item)) filtered.add(item); return filtered; } filter(numbers, new Function<Integer, Boolean>() { @Override public Boolean call(Integer value) { return value % 2 == 0; } });
160. Higher-order functions & lambdas public interface Function<T, R> { R call(T t); } public static <T> List<T> filter(Collection<T> items, Function<T, Boolean> f) { final List<T> filtered = new ArrayList<T>(); for (T item : items) if (f.call(item)) filtered.add(item); return filtered; } filter(numbers, new Function<Integer, Boolean>() { @Override public Boolean call(Integer value) { return value % 2 == 0; } }); Functional interface
161. Higher-order functions & lambdas public interface Function<T, R> { R call(T t); } public static <T> List<T> filter(Collection<T> items, Function<T, Boolean> f) { final List<T> filtered = new ArrayList<T>(); for (T item : items) if (f.call(item)) filtered.add(item); return filtered; } filter(numbers, new Function<Integer, Boolean>() { @Override public Boolean call(Integer value) { return value % 2 == 0; } }); Interface argument
162. Higher-order functions & lambdas public interface Function<T, R> { R call(T t); } public static <T> List<T> filter(Collection<T> items, Function<T, Boolean> f) { final List<T> filtered = new ArrayList<T>(); for (T item : items) if (f.call(item)) filtered.add(item); return filtered; } filter(numbers, new Function<Integer, Boolean>() { @Override public Boolean call(Integer value) { return value % 2 == 0; } }); Interface function call
163. Higher-order functions & lambdas public interface Function<T, R> { R call(T t); } public static <T> List<T> filter(Collection<T> items, Function<T, Boolean> f) { final List<T> filtered = new ArrayList<T>(); for (T item : items) if (f.call(item)) filtered.add(item); return filtered; } filter(numbers, new Function<Integer, Boolean>() { @Override public Boolean call(Integer value) { return value % 2 == 0; } }); Anonymous implementation
164. Higher-order functions & lambdas fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered }
165. Higher-order functions & lambdas fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered } filter(numbers, { value -> value % 2 == 0 })
166. Higher-order functions & lambdas fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered } filter(numbers, { value -> value % 2 == 0 })
167. Higher-order functions & lambdas fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered } filter(numbers, { value -> value % 2 == 0 }) Function type
168. Higher-order functions & lambdas fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered } filter(numbers, { value -> value % 2 == 0 }) Function call
169. Higher-order functions & lambdas fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered } filter(numbers, { value -> value % 2 == 0 }) Anonymous function
170. Higher-order functions & lambdas fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered }. filter(numbers, { value -> value % 2 == 0 } . )
171. Higher-order functions & lambdas fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered }. filter(numbers) { value -> value % 2 == 0 } .
172. Higher-order functions & lambdas fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered }. filter(numbers) { it % 2 == 0 } .
173. Higher-order functions & lambdas fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered }. filter(numbers) { it % 2 == 0 } .
174. Inline functions
175. Inline functions fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered }. filter(numbers) { it % 2 == 0 }
176. Inline functions inline fun <T> filter(items: Collection<T>, f: (T) -> Boolean): List<T> { val filtered = arrayListOf<T>() for (item in items) if (f(item)) filtered.add(item) return filtered }. filter(numbers) { it % 2 == 0 }
177. Inline functions val filtered = arrayListOf<T>() for (item in items) if (it % 2 == 0) filtered.add(item)
178. Inline functions fun call(f: () -> Unit) { f() } call { return }
179. Inline functions fun call(f: () -> Unit) { f() } call { return } Return not allowed
180. Inline functions fun call(f: () -> Unit) { f() }. call { return }.
181. Inline functions inline fun call(f: () -> Unit) { f() }. call { return }.
182. Inline functions inline fun call(f: () -> Unit) { f() }. call { return }. Return allowed
183. Inline functions inline fun <T : Any> View.findViewParent(): T? { var parent = getParent() while (parent != null && parent !is T) { parent = parent.getParent() } return parent as T }
184. Inline functions inline fun <T : Any> View.findViewParent(): T? { var parent = getParent() while (parent != null && parent !is T) { parent = parent.getParent() } return parent as T } Type erasure
185. Inline functions inline fun <T : Any> View.findViewParent(): T? { var parent = getParent() while (parent != null && parent !is T) { parent = parent.getParent() } return parent as T } Unchecked cast
186. Inline functions inline fun <T : Any> View.findViewParent(): T? { var parent = getParent() while (parent != null && parent !is T) { parent = parent.getParent() }. return parent as T }.
187. Inline functions inline fun <reified T : Any> View.findViewParent(): T? { var parent = getParent() while (parent != null && parent !is T) { parent = parent.getParent() }. return parent as T }. Reified type
188. Inline functions inline fun <reified T : Any> View.findViewParent(): T? { var parent = getParent() while (parent != null && parent !is T) { parent = parent.getParent() } return parent as T } Type check allowed
189. Inline functions inline fun <reified T : Any> View.findViewParent(): T? { var parent = getParent() while (parent != null && parent !is T) { parent = parent.getParent() } return parent as T } Type cast allowed
190. Extension functions
191. Extension functions public fun isLollipopOrGreater(code: Int): Boolean { return code >= Build.VERSION_CODES.LOLLIPOP }.
192. Extension functions public fun isLollipopOrGreater(code: Int): Boolean { return code >= Build.VERSION_CODES.LOLLIPOP }.
193. Extension functions public fun Int.isLollipopOrGreater(code: Int): Boolean { return code >= Build.VERSION_CODES.LOLLIPOP }.
194. Extension functions public fun Int.isLollipopOrGreater(): Boolean { return code >= Build.VERSION_CODES.LOLLIPOP }.
195. Extension functions public fun Int.isLollipopOrGreater(): Boolean {. return this >= Build.VERSION_CODES.LOLLIPOP }..
196. Extension functions public fun Int.isLollipopOrGreater(): Boolean {. return this >= Build.VERSION_CODES.LOLLIPOP }.. if (Build.VERSION.SDK_INT.isLollipopOrGreater) { // ... }.
197. Extension functions public fun Int.isLollipopOrGreater(): Boolean {. return this >= Build.VERSION_CODES.LOLLIPOP }. if (16.isLollipopOrGreater) { // ... }.
198. Extension functions final Function<Customer, Order> customerMapper = // ... final Function<Order, Boolean> orderFilter = // ... final Function<Order, Float> orderSorter = // ... final List<Order> vipOrders = sortBy(filter(map(customers, customerMapper), orderFilter), orderSorter);
199. Extension functions final Function<Customer, Order> customerMapper = // ... final Function<Order, Boolean> orderFilter = // ... final Function<Order, Float> orderSorter = // ... final List<Order> vipOrders = sortBy(filter(map(customers, customerMapper), orderFilter), orderSorter);
200. Extension functions final Function<Customer, Order> customerMapper = // ... final Function<Order, Boolean> orderFilter = // ... final Function<Order, Float> orderSorter = // ... final List<Order> vipOrders = sortBy(filter(map(customers, customerMapper), orderFilter), orderSorter);
201. Extension functions final Function<Customer, Order> customerMapper = // ... final Function<Order, Boolean> orderFilter = // ... final Function<Order, Float> orderSorter = // ... final List<Order> vipOrders = sortBy(filter(map(customers, customerMapper), orderFilter), orderSorter);
202. Extension functions final Function<Customer, Order> customerMapper = // ... final Function<Order, Boolean> orderFilter = // ... final Function<Order, Float> orderSorter = // ... final List<Order> vipOrders = sortBy(filter(map(customers, customerMapper), orderFilter), orderSorter);
203. Extension functions val vipOrders = customers .map { it.lastOrder } .filter { it.total >= 500F } .sortBy { it.total }
204. Extension functions val vipOrders = customers .map { it.lastOrder } .filter { it.total >= 500F } .sortBy { it.total }
205. Extension functions val vipOrders = customers .map { it.lastOrder } .filter { it.total >= 500F } .sortBy { it.total }
206. Extension functions val vipOrders = customers .map { it.lastOrder } .filter { it.total >= 500F } .sortBy { it.total }
207. Extension functions val vipOrders = customers .map { it.lastOrder } .filter { it.total >= 500F } .sortBy { it.total }
208. Extension functions val vipOrders = customers .map { it.lastOrder } .filter { it.total >= 500F } .sortBy { it.total }
209. Properties
210. Properties class Customer { private String firstName; private String lastName; private String email; public String getFirstName() { return firstName; } public String getLastName() { return lastName; } public String getEmail() { return email; } public void setFirstName(String firstName) { this.firstName = firstName } public void setLastName(String lastName) { this.lastName = lastName } public void setEmail(String email) { this.email = email } }
211. Properties class Customer { private String firstName; private String lastName; private String email; public String getFirstName() { return firstName; } public String getLastName() { return lastName; } public String getEmail() { return email; } public void setFirstName(String firstName) { this.firstName = firstName } public void setLastName(String lastName) { this.lastName = lastName } public void setEmail(String email) { this.email = email } }
212. Properties class Customer { private String firstName; private String lastName; private String email; public String getFirstName() { return firstName; } public String getLastName() { return lastName; } public String getEmail() { return email; } public void setFirstName(String firstName) { this.firstName = firstName } public void setLastName(String lastName) { this.lastName = lastName } public void setEmail(String email) { this.email = email } }
213. Properties class Customer { private String firstName; private String lastName; private String email; public String getFirstName() { return firstName; } public String getLastName() { return lastName; } public String getEmail() { return email; } public void setFirstName(String firstName) { this.firstName = firstName } public void setLastName(String lastName) { this.lastName = lastName } public void setEmail(String email) { this.email = email } }
214. Properties class Customer { var firstName: String = // ... var lastName: String = // ... var email: String = // ... }
215. Properties class Customer { var firstName: String = // ... var lastName: String = // ... var email: String = // ... } val customer = Customer() customer.firstName = "Michael" customer.lastName = "Pardo" customer.email = "michael@michaelpardo.com"
216. Primary constructors
217. Primary constructors class Customer {. var firstName: String = // ... var lastName: String = // ... var email: String = // ... }.
218. Primary constructors class Customer(firstName: String, lastName: String, email: String) {. var firstName: String = // ... var lastName: String = // ... var email: String = // ... }.
219. Primary constructors class Customer(firstName: String, lastName: String, email: String) {. var firstName: String = firstName var lastName: String = lastName var email: String = email }.
220. Primary constructors class Customer(firstName: String, lastName: String, email: String) {. var firstName: String var lastName: String var email: String init { this.firstName = firstName this.lastName = lastName this.email = email } }.
221. Primary constructors class Customer(firstName: String, lastName: String, email: String)
222. Primary constructors class Customer(var firstName: String, var lastName: String, var email: String)
223. Primary constructors class Customer( var firstName: String, var lastName: String, var email: String)
224. Primary constructors class Customer( val firstName: String, val lastName: String, val email: String)
225. Singletons
226. Singletons public class Singleton { private static volatile Singleton instance; private Singleton() { } public static Singleton getInstance() { if (instance == null ) { synchronized (Singleton.class) { if (instance == null) { instance = new Singleton(); } } } return instance; } }
227. Singletons public class Singleton { private static volatile Singleton instance = null; private Singleton() { } public static synchronized Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; } }
228. Singletons public class Singleton { private static final Singleton INSTANCE = new Singleton(); private Singleton() {} public static Singleton getInstance() { return INSTANCE; } }
229. Singletons public class Singleton { private static final Singleton instance; static { try { instance = new Singleton(); } catch (Exception e) { throw new RuntimeException("Darn, an error occurred!", e); } } public static Singleton getInstance() { return instance; } private Singleton() { } }
230. Singletons public class Singleton { private Singleton() { } private static class SingletonHolder { private static final Singleton INSTANCE = new Singleton(); } public static Singleton getInstance() { return SingletonHolder.INSTANCE; } }
231. Singletons public enum Singleton { INSTANCE; public void execute (String arg) { } }
232. Singletons object Singleton
233. Singletons object Logger { val tag = "TAG" fun d(message: String) { Log.d(tag, message) } }
234. Companion objects
235. Companion objects class LaunchActivity extends AppCompatActivity { public static final String TAG = LaunchActivity.class.getName(); public static void start(Context context) { context.startActivity(new Intent(context, LaunchActivity.class)); } }
236. Companion objects class LaunchActivity extends AppCompatActivity { public static final String TAG = LaunchActivity.class.getName(); public static void start(Context context) { context.startActivity(new Intent(context, LaunchActivity.class)); } }
237. Companion objects class LaunchActivity extends AppCompatActivity { public static final String TAG = LaunchActivity.class.getName(); public static void start(Context context) { context.startActivity(new Intent(context, LaunchActivity.class)); } }
238. Companion objects class LaunchActivity extends AppCompatActivity { public static final String TAG = LaunchActivity.class.getName(); public static void start(Context context) { context.startActivity(new Intent(context, LaunchActivity.class)); } } Timber.v("Starting activity %s", LaunchActivity.TAG);
239. Companion objects class LaunchActivity extends AppCompatActivity { public static final String TAG = LaunchActivity.class.getName(); public static void start(Context context) { context.startActivity(new Intent(context, LaunchActivity.class)); } } Timber.v("Starting activity %s", LaunchActivity.TAG); LaunchActivity.start(context);
240. Companion objects class LaunchActivity { companion object { val TAG: String = LaunchActivity::class.simpleName fun start(context: Context) { context.startActivity(Intent(context, LaunchActivity::class)) } } }
241. Companion objects class LaunchActivity { companion object { val TAG: String = LaunchActivity::class.simpleName fun start(context: Context) { context.startActivity(Intent(context, LaunchActivity::class)) } } }
242. Companion objects class LaunchActivity { companion object { val TAG: String = LaunchActivity::class.simpleName fun start(context: Context) { context.startActivity(Intent(context, LaunchActivity::class)) } } }
243. Companion objects class LaunchActivity { companion object { val TAG: String = LaunchActivity::class.simpleName fun start(context: Context) { context.startActivity(Intent(context, LaunchActivity::class)) } } }
244. Companion objects class LaunchActivity { companion object { val TAG: String = LaunchActivity::class.simpleName fun start(context: Context) { context.startActivity(Intent(context, LaunchActivity::class)) } } } Timber.v("Starting activity ${LaunchActivity.TAG}")
245. Companion objects class LaunchActivity { companion object { val TAG: String = LaunchActivity::class.simpleName fun start(context: Context) { context.startActivity(Intent(context, LaunchActivity::class)) } } } Timber.v("Starting activity ${LaunchActivity.TAG}") LaunchActivity.start(context)
246. Class delegation
247. Class delegation public class MyList<E> implements List<E> { private List<E> delegate; public MyList(delegate: List<E>) { this.delegate = delegate; } // ... public E get(int location) { return delegate.get(location) } // ... }
248. Class delegation public class MyList<E> implements List<E> { private List<E> delegate; public MyList(delegate: List<E>) { this.delegate = delegate; } // ... public E get(int location) { return delegate.get(location) } // ... }
249. Class delegation public class MyList<E> implements List<E> { private List<E> delegate; public MyList(delegate: List<E>) { this.delegate = delegate; } // ... public E get(int location) { return delegate.get(location) } // ... }
250. Class delegation public class MyList<E> implements List<E> { private List<E> delegate; public MyList(delegate: List<E>) { this.delegate = delegate; } // ... public E get(int location) { return delegate.get(location) } // ... }
251. Class delegation public class MyList<E> implements List<E> { private List<E> delegate; public MyList(delegate: List<E>) { this.delegate = delegate; } // ... public E get(int location) { return delegate.get(location) } // ... }
252. Class delegation class MyList<E>(list: List<E>) : List<E> by list
253. Class delegation class MyList<E>(list: List<E>) : List<E> by list
254. Class delegation class MyList<E>(list: List<E>) : List<E> by list
255. Class delegation class MyList<E>(list: List<E>) : List<E> by list
256. Declaration-site variance
257. Declaration-site variance String[] strings = { "hello", "world" }; Object[] objects = strings;
258. Declaration-site variance List<String> strings = Arrays.asList("hello", "world"); List<Object> objects = strings;
259. Declaration-site variance List<String> strings = Arrays.asList("hello", "world"); List<Object> objects = strings; Error: incompatible types
260. Declaration-site variance List<String> strings = Arrays.asList("hello", "world"); List<Object> objects = strings;
261. Declaration-site variance List<String> strings = Arrays.asList("hello", "world"); List<? extends Object> objects = strings;
262. Declaration-site variance public interface List<E> extends Collection<E> { public boolean addAll(Collection<? extends E> collection); public E get(int location); }
263. Declaration-site variance public interface List<out E> : Collection<E> { public fun get(index: Int): E } public interface MutableList<E> : List<E>, MutableCollection<E> { override fun addAll(c: Collection<E>): Boolean }
264. Declaration-site variance public interface List<out E> : Collection<E> { public fun get(index: Int): E } public interface MutableList<E> : List<E>, MutableCollection<E> { override fun addAll(c: Collection<E>): Boolean }
265. Declaration-site variance public interface List<out E> : Collection<E> { public fun get(index: Int): E } public interface MutableList<E> : List<E>, MutableCollection<E> { override fun addAll(c: Collection<E>): Boolean }
266. Declaration-site variance val strings: List<String> = listOf("hello", "world") val objects: List<Any> = strings
267. Declaration-site variance val strings: List<String> = arrayListOf("hello", "world") val objects: List<Any> = strings
268. Declaration-site variance val strings: MutableList<String> = arrayListOf("hello", "world") val objects: List<Any> = strings
269. Declaration-site variance val strings: MutableList<String> = arrayListOf("hello", "world") val objects: MutableList<Any> = strings
270. Declaration-site variance val strings: MutableList<String> = arrayListOf("hello", "world") val objects: MutableList<Any> = strings Type mismatch
271. Operator overloading
272. Operator overloading enum class Coin(val cents: Int) { PENNY(1), NICKEL(5), DIME(10), QUARTER(25), }
273. Operator overloading enum class Coin(val cents: Int) { PENNY(1), NICKEL(5), DIME(10), QUARTER(25), }. class Purse(var amount: Float)
274. Operator overloading enum class Coin(val cents: Int) { PENNY(1), NICKEL(5), DIME(10), QUARTER(25), }. class Purse(var amount: Float) { fun plusAssign(coin: Coin): Unit { amount += (coin.cents / 100f) } } Reserved function name
275. Operator overloading enum class Coin(val cents: Int) { PENNY(1), NICKEL(5), DIME(10), QUARTER(25), } class Purse(var amount: Float) { fun plusAssign(coin: Coin): Unit { amount += (coin.cents / 100f) } } var purse = Purse(1.50f)
276. Operator overloading enum class Coin(val cents: Int) { PENNY(1), NICKEL(5), DIME(10), QUARTER(25), } class Purse(var amount: Float) { fun plusAssign(coin: Coin): Unit { amount += (coin.cents / 100f) } } var purse = Purse(1.50f) purse += Coin.QUARTER // 1.75
277. Operator overloading enum class Coin(val cents: Int) { PENNY(1), NICKEL(5), DIME(10), QUARTER(25), } class Purse(var amount: Float) { fun plusAssign(coin: Coin): Unit { amount += (coin.cents / 100f) } } var purse = Purse(1.50f) purse += Coin.QUARTER // 1.75 purse += Coin.DIME // 1.85
278. Operator overloading enum class Coin(val cents: Int) { PENNY(1), NICKEL(5), DIME(10), QUARTER(25), } class Purse(var amount: Float) { fun plusAssign(coin: Coin): Unit { amount += (coin.cents / 100f) } } var purse = Purse(1.50f) purse += Coin.QUARTER // 1.75 purse += Coin.DIME // 1.85 purse += Coin.PENNY // 1.86
279. Operator overloading a + b a - b a * b a / b a % b a == b a != b a +- b a -= b a *= b a /= b a %= b a > b a < b a >= b a <= b a++ a-- a[] a() a..b a in b a !in b
280. Adding Kotlin to your project
281. app └── src └── main ├── java └── kotlin
282. app └── src └── main ├── java └── kotlin
283. buildscript { repositories { mavenCentral() } dependencies { classpath 'org.jetbrains.kotlin:kotlin-gradle-plugin:<version>' } } apply plugin "kotlin-android" sourceSets { main.kotlin.srcDirs += 'src/main/myKotlin' } repositories { mavenCentral() } dependencies { compile 'org.jetbrains.kotlin:kotlin-stdlib:<version>' }
284. buildscript { repositories { mavenCentral() } dependencies { classpath 'org.jetbrains.kotlin:kotlin-gradle-plugin:<version>' } } apply plugin "kotlin-android" sourceSets { main.kotlin.srcDirs += 'src/main/myKotlin' } repositories { mavenCentral() } dependencies { compile 'org.jetbrains.kotlin:kotlin-stdlib:<version>' }
285. buildscript { repositories { mavenCentral() } dependencies { classpath 'org.jetbrains.kotlin:kotlin-gradle-plugin:<version>' } } apply plugin "kotlin-android" sourceSets { main.kotlin.srcDirs += 'src/main/myKotlin' } repositories { mavenCentral() } dependencies { compile 'org.jetbrains.kotlin:kotlin-stdlib:<version>' }
286. buildscript { repositories { mavenCentral() } dependencies { classpath 'org.jetbrains.kotlin:kotlin-gradle-plugin:<version>' } } apply plugin "kotlin-android" sourceSets { main.kotlin.srcDirs += 'src/main/myKotlin' } repositories { mavenCentral() } dependencies { compile 'org.jetbrains.kotlin:kotlin-stdlib:<version>' }
288. Resources • http://kotlinlang.org/docs/reference/ • http://kotlinlang.org/docs/tutorials/koans.html • http://kotlinlang.org/docs/reference/comparison-to-java.html
289. Questions? @pardom