Kotlinで抽象クラスを定義する構文と具体的な使用例を徹底解説

abstract class Animal {
    abstract fun sound() // 抽象メソッド
    fun breathe() {      // 具体的なメソッド
        println("Breathing...")
    }
}

class Dog : Animal() {
    override fun sound() {
        println("Woof! Woof!")
    }
}

class Cat : Animal() {
    override fun sound() {
        println("Meow!")
    }
}

fun main() {
    val dog = Dog()
    dog.sound()   // 出力: Woof! Woof!
    dog.breathe() // 出力: Breathing...

    val cat = Cat()
    cat.sound()   // 出力: Meow!
    cat.breathe() // 出力: Breathing...
}

abstract class Animal {
    // 抽象メソッド（未実装）
    abstract fun makeSound()

    // 具体的メソッド（共通の実装）
    fun sleep() {
        println("Sleeping...")
    }
}

class Dog : Animal() {
    override fun makeSound() {
        println("Woof! Woof!")
    }
}

class Cat : Animal() {
    override fun makeSound() {
        println("Meow!")
    }
}

fun main() {
    val dog = Dog()
    dog.makeSound()  // 出力: Woof! Woof!
    dog.sleep()      // 出力: Sleeping...

    val cat = Cat()
    cat.makeSound()  // 出力: Meow!
    cat.sleep()      // 出力: Sleeping...
}

abstract class Animal {
    abstract fun makeSound()
    fun eat() {
        println("Eating...")
    }
}

abstract class Task {
    fun execute() {
        start()
        process()
        end()
    }
    abstract fun process()
    fun start() { println("Starting task") }
    fun end() { println("Ending task") }
}

abstract class Payment {
    fun authenticate() {
        println("Authenticating payment")
    }
    abstract fun pay(amount: Double)
}

abstract class Vehicle(val color: String) {
    abstract fun drive()
}

abstract class Animal(val name: String) {
    // 抽象メソッド: 各動物ごとに異なる鳴き声を実装
    abstract fun makeSound()

    // 具体的メソッド: すべての動物に共通する動作
    fun sleep() {
        println("$name is sleeping.")
    }
}

class Dog(name: String) : Animal(name) {
    override fun makeSound() {
        println("$name says: Woof! Woof!")
    }
}

class Cat(name: String) : Animal(name) {
    override fun makeSound() {
        println("$name says: Meow!")
    }
}

fun main() {
    val dog = Dog("Buddy")
    dog.makeSound()  // 出力: Buddy says: Woof! Woof!
    dog.sleep()      // 出力: Buddy is sleeping.

    val cat = Cat("Whiskers")
    cat.makeSound()  // 出力: Whiskers says: Meow!
    cat.sleep()      // 出力: Whiskers is sleeping.
}

// 抽象クラス: 動物の基本的な特徴を定義
abstract class Animal(val name: String) {
    abstract fun makeSound()
    fun eat() {
        println("$name is eating.")
    }
}

// インターフェース: ペットとしての振る舞いを定義
interface Pet {
    fun play()
}

// サブクラス: 犬としての特徴を定義し、Petインターフェースを実装
class Dog(name: String) : Animal(name), Pet {
    override fun makeSound() {
        println("$name says: Woof! Woof!")
    }

    override fun play() {
        println("$name is playing fetch.")
    }
}

// サブクラス: 猫としての特徴を定義し、Petインターフェースを実装
class Cat(name: String) : Animal(name), Pet {
    override fun makeSound() {
        println("$name says: Meow!")
    }

    override fun play() {
        println("$name is playing with a ball of yarn.")
    }
}

fun main() {
    val dog = Dog("Buddy")
    dog.makeSound() // 出力: Buddy says: Woof! Woof!
    dog.eat()       // 出力: Buddy is eating.
    dog.play()      // 出力: Buddy is playing fetch.

    val cat = Cat("Whiskers")
    cat.makeSound() // 出力: Whiskers says: Meow!
    cat.eat()       // 出力: Whiskers is eating.
    cat.play()      // 出力: Whiskers is playing with a ball of yarn.
}

Class 'Dog' is not abstract and does not implement abstract member 'makeSound()' in 'Animal'

abstract class Animal {
    abstract fun makeSound()
}

class Dog : Animal() {
    override fun makeSound() {
        println("Woof! Woof!")
    }
}

Cannot create an instance of an abstract class

abstract class Animal {
    abstract fun makeSound()
}

class Dog : Animal() {
    override fun makeSound() {
        println("Woof!")
    }
}

// 正しいインスタンス化
val dog = Dog()
dog.makeSound()

Constructor 'Animal(String)' is not accessible in this context

abstract class Animal(val name: String) {
    abstract fun makeSound()
}

class Dog(name: String) : Animal(name) {
    override fun makeSound() {
        println("$name says: Woof!")
    }
}

val dog = Dog("Buddy")
dog.makeSound()  // 出力: Buddy says: Woof!

Property 'color' must be initialized or be abstract

abstract class Vehicle {
    abstract val color: String
}

class Car : Vehicle() {
    override val color: String = "Red"
}

val car = Car()
println(car.color)  // 出力: Red

Class 'Hybrid' cannot inherit from multiple classes

abstract class Engine {
    abstract fun start()
}

interface Transmission {
    fun shiftGear()
}

class Car : Engine(), Transmission {
    override fun start() {
        println("Engine starting...")
    }

    override fun shiftGear() {
        println("Shifting gear...")
    }
}

abstract class Animal {
    abstract fun makeSound()
}

class Dog : Animal() {
    override fun makeSound() {
        println("Woof!")
    }
}

class Cat : Animal() {
    override fun makeSound() {
        println("Meow!")
    }
}

fun main() {
    val dog = Dog()
    val cat = Cat()

    dog.makeSound() // 出力: Woof!
    cat.makeSound() // 出力: Meow!
}

abstract class Vehicle {
    abstract val speed: Int
    fun displaySpeed() {
        println("Speed: $speed km/h")
    }
}

class Car : Vehicle() {
    override val speed: Int = 120
}

class Bike : Vehicle() {
    override val speed: Int = 30
}

fun main() {
    val car = Car()
    val bike = Bike()

    car.displaySpeed() // 出力: Speed: 120 km/h
    bike.displaySpeed() // 出力: Speed: 30 km/h
}

abstract class Appliance {
    fun turnOn() {
        println("The appliance is now ON.")
    }
}

interface WiFiEnabled {
    fun connectToWiFi()
}

class SmartLight : Appliance(), WiFiEnabled {
    override fun connectToWiFi() {
        println("Smart Light connected to WiFi.")
    }
}

fun main() {
    val smartLight = SmartLight()
    smartLight.turnOn()        // 出力: The appliance is now ON.
    smartLight.connectToWiFi() // 出力: Smart Light connected to WiFi.
}