Kotlin For Android - Constructors and Control Flow (part 2 of 7)

Kotlin for Android May 24, 2018 y/kotlin-workbook

Objects, Constructors and Control Flow y/kotlin-workbook

classes BASIC SYNTAX y/kotlin-workbook interface Runnable { fun run() } interface RepeatingRunnable : Runnable { fun run(times: Int) { (1..times).forEach { run() } } } open class Greeting : Runnable { override fun run() = println("Hi!") } class RepeatingGreeting : Greeting(), RepeatingRunnable RepeatingGreeting().run(3)

● One primary constructor as part of class declaration ○ Declare property visibility and default values in the parameter list constructors OBJECTS AND FLOW y/kotlin-workbook class Person( val name: String = "John", private var age: Int )

● One primary constructor as part of class declaration ○ Declare property visibility and default values in the parameter list ● Initialization blocks - init constructors OBJECTS AND FLOW y/kotlin-workbook class Person( val name: String = "John", private var age: Int ){ init { // Initialize things here... } }

● One primary constructor as part of class declaration ○ Declare property visibility and default values in the parameter list ● Initialization blocks - init ● Optional secondary constructors ● Property initialization constructors OBJECTS AND FLOW y/kotlin-workbook class Person( val name: String = "John", private var age: Int ){ var hairColor: Color = Color.BLACK init { // Initialize things here... } constructor(age: Int, hairColor: Color): this(age = age){ this.hairColor = hairColor } }

constructors OBJECTS AND FLOW y/kotlin-workbook DEMO

object OBJECTS AND FLOW y/kotlin-workbook ● Used to create anonymous inner classes and singletons ● Can have static methods in the JVM ● Can have static fields in the JVM ● Every class can have a companion object ● Cannot inherit from object ○ object can inherit and extend though

object OBJECTS AND FLOW y/kotlin-workbook object Foo { val BAR = "BAR" fun hi() = "hi" } // kotlin val bar = Foo.BAR val foo = Foo.hi() // java String bar = Foo.INSTANCE.BAR; String foo = Foo.INSTANCE.hi();

object OBJECTS AND FLOW y/kotlin-workbook object Foo { const val BAR = "BAR" @JvmStatic fun hi() = "hi" } // kotlin val bar = Foo.BAR val foo = Foo.hi() // java String bar = Foo.INSTANCE.BAR; String foo = Foo.INSTANCE.hi(); // java improved interop String bar = Foo.BAR; String foo = Foo.hi();

companion object advanced OBJECTS AND FLOW y/kotlin-workbook UserRepo.intance() // returns the real repo BizRepo.intance() // returns the real repo UserRepo.mock = mock(UserRepo) BizRepo.mock = mock(BizRepo) UserRepo.intance() // returns the mock repo BizRepo.intance() // returns the mock repo UserRepo.mock = null BizRepo.mock = null UserRepo.intance() // returns the real repo BizRepo.intance() // returns the real repo

companion object advanced OBJECTS AND FLOW y/kotlin-workbook interface Factory<T: Any> { var mock: T? fun instance(): T } UserRepo.intance() // returns the real repo BizRepo.intance() // returns the real repo UserRepo.mock = mock(UserRepo) BizRepo.mock = mock(BizRepo) UserRepo.intance() // returns the mock repo BizRepo.intance() // returns the mock repo UserRepo.mock = null BizRepo.mock = null UserRepo.intance() // returns the real repo BizRepo.intance() // returns the real repo

companion object advanced OBJECTS AND FLOW y/kotlin-workbook interface Factory<T: Any> { var mock: T? fun instance(): T } open class Provider<T: Any>(init: () -> T): Factory<T> { override var mock: T? = null private val instance: T by lazy(init) override fun instance() = mock ?: instance } UserRepo.intance() // returns the real repo BizRepo.intance() // returns the real repo UserRepo.mock = mock(UserRepo) BizRepo.mock = mock(BizRepo) UserRepo.intance() // returns the mock repo BizRepo.intance() // returns the mock repo UserRepo.mock = null BizRepo.mock = null UserRepo.intance() // returns the real repo BizRepo.intance() // returns the real repo

companion object advanced OBJECTS AND FLOW y/kotlin-workbook interface Factory<T: Any> { var mock: T? fun instance(): T } open class Provider<T: Any>(init: () -> T): Factory<T> { override var mock: T? = null private val instance: T by lazy(init) override fun instance() = mock ?: instance } class UserRepo { companion object : Provider<UserRepo>({ UserRepo() }) } class BizRepo { companion object : Provider<BizRepo>({ BizRepo() }) } UserRepo.intance() // returns the real repo BizRepo.intance() // returns the real repo UserRepo.mock = mock(UserRepo) BizRepo.mock = mock(BizRepo) UserRepo.intance() // returns the mock repo BizRepo.intance() // returns the mock repo UserRepo.mock = null BizRepo.mock = null UserRepo.intance() // returns the real repo BizRepo.intance() // returns the real repo

● No goto Control Flow OBJECTS AND FLOW y/kotlin-workbook

Control Flow OBJECTS AND FLOW y/kotlin-workbook fun foo() { listOf(1, 2, 3, 4, 5).forEach { if (it == 3) return print(it) } println(" this is unreachable") } ● No goto ● return, break and continue

Control Flow OBJECTS AND FLOW y/kotlin-workbook fun foo() { listOf(1, 2, 3, 4, 5).forEach { if (it == 3) return print(it) } println(" this is unreachable") } // 12 ● No goto ● return, break and continue

Control Flow OBJECTS AND FLOW y/kotlin-workbook fun foo() { listOf(1, 2, 3, 4, 5).forEach { if (it == 3) return@forEach print(it) } println(" this is reachable") } ● No goto ● return, break and continue can use labels

Control Flow OBJECTS AND FLOW y/kotlin-workbook fun foo() { listOf(1, 2, 3, 4, 5).forEach { if (it == 3) return@forEach print(it) } println(" this is reachable") } // 1245 this is reachable ● No goto ● return, break and continue can use labels

Control Flow OBJECTS AND FLOW y/kotlin-workbook fun foo() { listOf(1, 2, 3, 4, 5).forEach loop@{ if (it == 3) return@loop print(it) } println(" this is reachable") } // 1245 this is reachable ● No goto ● return, break and continue can use labels

Control Flow OBJECTS AND FLOW y/kotlin-workbook fun foo() { listOf(1, 2, 3, 4, 5).run { forEach { if (it == 3) return@run print(it) }} println(" this is reachable") } // 12 this is reachable ● No goto ● return, break and continue can use labels

Control Flow OBJECTS AND FLOW y/kotlin-workbook fun foo() { for (int in listOf(1, 2, 3, 4, 5)) { if (int == 3) break print(int) } println(" this is reachable") } ● No goto ● return, break and continue can use labels ● for loop - no parameterized for(;;)

Control Flow OBJECTS AND FLOW y/kotlin-workbook ● No goto ● return, break and continue can use labels ● for loop - no parametrized for(;;) ● while - same as java

Control Flow OBJECTS AND FLOW y/kotlin-workbook return if (isJvmRuntime) { RuntimeEnvironment.application } else { InstrumentationRegistry.getContext() } ● No goto ● return, break and continue can use labels ● for loop - no parametrized for(;;) ● while - same as java ● if - same as java, can be used as an expression

Control Flow OBJECTS AND FLOW y/kotlin-workbook return when (isJvmRuntime) { true -> RuntimeEnvironment.application else -> InstrumentationRegistry.getContext() } ● No goto ● return, break and continue can use labels ● for loop - no parametrized for(;;) ● while - same as java ● if - same as java, can be used as an expression ● when - replaces switch from java, can be used as expr.

Control Flow OBJECTS AND FLOW y/kotlin-workbook val z = when { x.isOdd() -> "x is odd" y.isEven() -> "y is even" else -> "x is funny, y is cool" } ● No goto ● return, break and continue can use labels ● for loop - no parametrized for(;;) ● while - same as java ● if - same as java, can be used as an expression ● when - replaces switch from java, can be used as expr.

Control Flow OBJECTS AND FLOW y/kotlin-workbook val isJvmRuntime = try { Class.forName("org.robolectric.RuntimeEnvironment") true } catch (notFound: ClassNotFoundException) { false } ● No goto ● return, break and continue can use labels ● for loop - no parametrized for(;;) ● while - same as java ● if - same as java, can be used as an expression ● when - replaces switch from java, can be used as expr. ● try catch - same as java, can be used as an expression

Kotlin For Android - Constructors and Control Flow (part 2 of 7)

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