不会真的学不会kotlin吧？类型进阶

代码部分参考慕课网新kotlin入门课程

本章简介

这一章主要就是要注意java类和kotlin类的区别一些的，看看知道怎么用就可以了

结构导图

类的构造器

java

public class Person { private int age; private String name; public Person(int age, String name) { this.age = age; this.name = name; } { System.out.println("1"); } { System.out.println("2"); } } 

kotlin

abstract class Animal class Person(var age: Int, var name: String = "unknown") { override fun equals(other: Any?) = (other as? Person)?.name?.equals(name) ?: false override fun hashCode() = name.hashCode() } val persons = HashMap<String, Person>() fun Person(name: String): Person { return persons[name] ?: Person(1, name).also { persons[name] = it } } 

成员可见性

可见性类型	Java	Kotlin
public	公开	与Java相同,默认
internal	X	模块内可见
default	包内可见，默认	X
protected	包内及子类可见	类内及子类可见
private	类内可见	类或文件内可见

可见性类型	*声明	类	成员
public	V	V	V
internal	V,模块	V,模块	V,模块
protected	X	X	V
private	V,文件	V，文件	V,类

类属性的初始化

方案名称	推荐指数	理由
可空类型	1	增加代码复杂度﹔初始化与声明分离; 调用处需要做判空处理
lateinit	2	初始化与声明分离;调用处虽无需判空 处理，但潜在的初始化问题可能被掩盖
lazy	3	初始化与声明内聚;无需声明可空类型

代理 Delegates

kotlin

//region api interface Api { fun a() fun b() fun c() } class ApiImpl : Api { override fun a() {} override fun b() {} override fun c() {} } class ApiWrapper(val api: Api) : Api by api { override fun c() { println("c is called.") api.c() } } //endregion class SuperArray<E>( private val list: MutableList<E?> = ArrayList(), private val map: MutableMap<Any, E> = HashMap() ) : MutableList<E?> by list, MutableMap<Any, E> by map { override fun isEmpty() = list.isEmpty() && map.isEmpty() override val size: Int get() = list.size + map.size override fun clear() { list.clear() map.clear() } override operator fun set(index: Int, element: E?): E? { if (list.size <= index) { repeat(index - list.size + 1) { list.add(null) } } return list.set(index, element) } override fun toString(): String { return """List: [$list]; Map: [$map]""" } } fun main() { val superArray = SuperArray<String>() val superArray2 = SuperArray<String>() superArray += "Hello" superArray["Hello"] = "World" superArray2[superArray] = "World" superArray[1] = "world" superArray[4] = "!!!" println(superArray) println(superArray2) } 

kotlin

class Person(val name: String){ val firstName by lazy { name.split(" ")[0] } val lastName by lazy { name.split(" ")[1] } } class StateManager { var state: Int by Delegates.observable(0) { property, oldValue, newValue -> println("State changed from $oldValue -> $newValue") } } class Foo { val x: Int by X() var y: Int by X() } class X { operator fun getValue(thisRef: Any?, property: KProperty<*>): Int { return 2 } operator fun setValue(thisRef: Any?, property: KProperty<*>, i: Int) { } } fun main() { val stateManager = StateManager() stateManager.state = 3 stateManager.state = 4 println(Foo().x) } 

单例

java

public class Singleton { public static final Singleton INSTANCE = new Singleton(); } 

kotlin

object Singleton: Runnable{ override fun run() { } @JvmField var x: Int = 2 @JvmStatic fun y(){ } init { } } class Foo { companion object { @JvmField var x: Int = 2 @JvmStatic fun y(){ } } } fun main() { Singleton.x
    Singleton.y() val foo = Foo() } 

data class数据类

	JavaBean	dataclass
构造方法	默认无参构造	属性作为参数
字段	字段私有,Getter/Setter公开	属性
继承性	可继承也可被继承	不可被继承
component	无	相等性、解构等

java

public class Book { private long id; private String name; private Person person; public long getId() { return id; } public Book id(long id) { this.id = id; return this; } public String getName() { return name; } public Book name(String name) { this.name = name; return this; } public Person getPerson() { return person; } public Book person(Person person) { this.person = person; return this; } } 

kotlin

@PoKo data class Book(val id: Long, val name: String, val author: Person) { } data class Person(val id: Long, val name: String, val age: Int) fun main() { //    val book = Book(0, "Kotlin in Action", Person(1, "Dmitry", 40)) //    book.copy()  val id = book.component1()  val name = book.component2()  val author = book.component3() // //    val (id, name, author) = book // //    val pair = "Hello" to "World" //    val (hello, world) = pair val book = Book::class.java.newInstance() } 

内部类

java

public class Outer { class Inner { } static class StaticInner { } } 

kotlin

class Outer { inner class Inner class StaticInner } object OuterObject { object StaticInnerObject } fun main() { val inner = Outer().Inner() val staticInner = Outer.StaticInner() } 

枚举类

java

public class JavaEnums { enum State implements Runnable { Idle { @Override public void run() { } }, Busy { @Override public void run() { } }; } public static void main(String... args) { System.out.println(State.Idle.getClass().getSuperclass().getSuperclass()); System.out.println(State.Idle.name()); // Idle System.out.println(State.Idle.ordinal()); // 0 } } 

kotlin

enum class State: Runnable{ Idle, Busy{ override fun run() { println("For Busy State.") } }; override fun run() { println("For  Every State.") } } //region fold fun State.successor(): State? { return State.values().let { if (ordinal + 1 >= it.size) null else it[ordinal + 1] } } fun State.predecessor(): State? { return State.values().let { if (ordinal - 1 < 0) null else it[ordinal - 1] } } enum class Color { White, Red, Green, Blue, Yellow, Black } //endregion fun main() { State.Idle.run() State.Busy.run() println(State.Idle.successor()) println(State.Busy.successor()) State.Idle.name // Idle State.Idle.ordinal // 0 val state = State.Idle val value = when (state) { State.Idle -> { 0 } State.Busy -> { 1 } } if(state <= State.Idle){ } val colorRange = Color.White .. Color.Green val color = Color.Blue println(color in colorRange) } 

密封类

kotlin

//region entity data class Song(val name: String, val url: String, var position: Int) data class ErrorInfo(val code: Int, val message: String) object Songs { val StarSky = Song("Star Sky", "https://fakeurl.com/321144.mp3", 0) } //endregion //region state sealed class PlayerState object Idle : PlayerState() class Playing(val song: Song) : PlayerState() { fun start() {} fun stop() {} } class Error(val errorInfo: ErrorInfo) : PlayerState() { fun recover() {} } //endregion class Player { var state: PlayerState = Idle fun play(song: Song) { this.state = when (val state = this.state) { Idle -> { Playing(song).also(Playing::start) } is Playing -> { state.stop() Playing(song).also(Playing::start) } is Error -> { state.recover() Playing(song).also(Playing::start) } } } } fun main() { val player = Player() player.play(Songs.StarSky) } 

内联类

kotlin

inline class BoxInt(val value: Int): Comparable<Int> { override fun compareTo(other: Int) = value.compareTo(other) operator fun inc(): BoxInt { return BoxInt(value + 1) } } inline class State(val ordinal: Int) { companion object { val Idle = State(0) val Busy = State(1) } fun values() = arrayOf(Idle, Busy) val name: String get() = when (this) { State.Idle -> "Idle" State.Busy -> "Busy" else -> throw IllegalArgumentException() } } inline class Color(val value: UInt) { companion object { val Red = Color(0xFFFF0000u) val Green = Color(0xFF00FF00u) val Blue = Color(0xFF0000FFu) } fun values() = arrayOf(Red, Green, Blue) val name: String get() = when (this) { Red -> "Red" Green -> "Green" Blue -> "Blue" else -> throw IllegalArgumentException() } } fun main() { var boxInt = BoxInt(5) if(boxInt < 10){ println("value is less than 10") } val newValue = boxInt.value * 200 println(newValue) boxInt++ println(boxInt) //优化 var value = 5 val newValue = value * 200 BoxInt.inc-imlp(value) printLn(BoxInt(value)) } 

EG

kotlin

class PropertiesDelegate(private val path: String, private val defaultValue: String = ""){ private lateinit var url: URL private val properties: Properties by lazy { val prop = Properties() url = try { javaClass.getResourceAsStream(path).use { prop.load(it) } javaClass.getResource(path) } catch (e: Exception) { try { ClassLoader.getSystemClassLoader().getResourceAsStream(path).use { prop.load(it) } ClassLoader.getSystemClassLoader().getResource(path)!! } catch (e: Exception) { FileInputStream(path).use { prop.load(it) } URL("file://${File(path).canonicalPath}") } } prop } operator fun getValue(thisRef: Any?, property: KProperty<*>): String { return properties.getProperty(property.name, defaultValue) } operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) { properties.setProperty(property.name, value) File(url.toURI()).outputStream().use { properties.store(it, "Hello!!") } } } abstract class AbsProperties(path: String){ protected val prop = PropertiesDelegate(path) } class Config: AbsProperties("Config.properties"){ var author by prop var version by prop var desc by prop } fun main() { val config = Config() println(config.author) config.author = "Bennyhuo" println(config.author) } 

sealed class IntList { object Nil: IntList() { override fun toString(): String { return "Nil" } } data class Cons(val head: Int, val tail: IntList): IntList(){ override fun toString(): String { return "$head, $tail" } } fun joinToString(sep: Char = ','): String { return when(this){ Nil -> "Nil" is Cons -> { "${head}$sep${tail.joinToString(sep)}" } } } } fun IntList.sum(): Int { return when(this){ IntList.Nil -> 0 is IntList.Cons -> head + tail.sum() } } operator fun IntList.component1(): Int? { return when(this){ IntList.Nil -> null is IntList.Cons -> head } } operator fun IntList.component2(): Int? { return when(this){ IntList.Nil -> null is IntList.Cons -> tail.component1() } } operator fun IntList.component3(): Int? { return when(this){ IntList.Nil -> null is IntList.Cons -> tail.component2() } } fun intListOf(vararg ints: Int): IntList { return when(ints.size){ 0 -> IntList.Nil else -> { IntList.Cons( ints[0], intListOf(*(ints.slice(1 until ints.size).toIntArray())) ) } } } // [0, 1, 2, 3] fun main() { //val list = IntList.Cons(0, IntList.Cons(1,  IntList.Cons(2,  IntList.Cons(3, IntList.Nil)))) val list = intListOf(0, 1, 2, 3) println(list) println(list.joinToString('-')) println(list.sum()) val (first, second, third) = list println(first) println(second) println(third) //val (a, b, c, d, e) = listOf<Int>() } 

本文地址：https://blog.csdn.net/qq_35928566/article/details/108020849