快速上手kotlin接口抽象类及泛型
Posted super码王
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接口定义
kotlin规定所有的接口属性和函数实现都要使用 override 关键字,接口中定义的函数并不需要open关键字修饰,他们默认就是open的
代码展示:
package com.wustyq.kotlinstudy
interface Movable
var maxSpeed: Int
var wheels: Int
fun move(movable: Movable): String
class Car(name: String, override var wheels: Int = 4) : Movable
override var maxSpeed: Int
get() = TODO("Not yet implemented")
set(value)
override fun move(movable: Movable): String
TODO("Not yet implemented")
- 接口里的属性和方法都得实现
- 属性实现可以选择在构造方法里,也可以不在构造方法里,如果不在构造方法里,就得设置get和set方法
默认实现
我们也可以在接口里提供默认属性的getter方法和函数实现
代码示例:
package com.wustyq.kotlinstudy
interface Movable
val maxSpeed: Int
get() = (0..4).shuffled()
.last()
var wheels: Int
fun move(movable: Movable): String
class Car(name: String, override var wheels: Int = 4) : Movable
override var maxSpeed: Int
get() = super.maxSpeed
set(value)
override fun move(movable: Movable): String
TODO("Not yet implemented")
- 接口里属性修饰符是val,接口里属性必须提供get方法
- 接口里属性修饰符是val,实现类可以是val 或 var,如果是val就不用set方法,如果是var,就得set和get一起
抽象类
要定义一个抽象类,你需要在定义之前加上 abstract 关键字,除了具体的函数实现,抽象类也可以包含抽象函数---只有定义,没有函数实现。
代码示例:
package com.wustyq.kotlinstudy
abstract class Gun(val range: Int)
//抽象类里面既有具体实现方法
protected fun doSomething()
println("doSomething")
//也存在抽象方法,继承该抽象类的类要实现这个方法
abstract fun pullTrigger(): String
class AK47(val price: Int) : Gun(range = 500)
override fun pullTrigger(): String
TODO("Not yet implemented")
定义泛型类型
代码展示:
package com.wustyq.kotlinstudy
class MagicBox<T>(item: T)
private var subject: T = item
class Boy(val name: String, val age: Int)
class Dog(val weight: Int)
fun main()
val box1: MagicBox<Boy> = MagicBox(Boy("Jack", 20))
val box2: MagicBox<Dog> = MagicBox(Dog(20))
泛型函数
代码展示:
package com.wustyq.kotlinstudy
class MagicBox<T>(item: T)
var available = false
private var subject: T = item
fun fetch(): T?
return subject.takeIf available
class Boy(val name: String, val age: Int)
class Dog(val weight: Int)
fun main()
val box1: MagicBox<Boy> = MagicBox(Boy("Jack", 20))
val box2: MagicBox<Dog> = MagicBox(Dog(20))
box1.available = true
println(box1.fetch()?.name)
效果展示:
多泛型参数
代码示例:
package com.wustyq.kotlinstudy
import javax.security.auth.Subject
class MagicBox<T>(item: T)
var available = false
private var subject: T = item
fun fetch(): T?
return subject.takeIf available
fun <R> fetch(subjectModFunction: (T) -> R): R?
return subjectModFunction(subject).takeIf available
class Boy(val name: String, val age: Int)
class Dog(val weight: Int)
fun main()
val box1: MagicBox<Boy> = MagicBox(Boy("Jack", 20))
val box2: MagicBox<Dog> = MagicBox(Dog(20))
box1.available = true
println(box1.fetch()?.age)
val boy3 = box1.fetch
Boy(it.name, it.age + 10)
println(boy3?.age)
效果展示:
泛型类型约束
代码示例:
package com.wustyq.kotlinstudy
import javax.security.auth.Subject
class MagicBox<T : Human>(item: T)
var available = false
private var subject: T = item
fun fetch(): T?
return subject.takeIf available
fun <R> fetch(subjectModFunction: (T) -> R): R?
return subjectModFunction(subject).takeIf available
open class Human(val age: Int)
class Boy(val name: String, age: Int) : Human(age)
class Dog(val weight: Int)
fun main()
val box1: MagicBox<Boy> = MagicBox(Boy("Jack", 20))
val box2: MagicBox<Dog> = MagicBox(Dog(20))
box1.available = true
println(box1.fetch()?.age)
val boy3 = box1.fetch
Boy(it.name, it.age + 10)
println(boy3?.age)
效果展示:
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