Kotlinで複数のデータ型を持つ構造体の定義方法を完全解説

val name: String? = null

val number = 10  // Int型として推論される
val message = "Hello"  // String型として推論される

data class Person(val name: String, val age: Int, val score: Double)

   val person1 = Person("Alice", 25, 95.0)
   val person2 = person1.copy(age = 26)  // ageのみ変更

   val (name, age, score) = person1
   println(name)  // 出力: Alice

data class Product(val id: Int, val name: String, val price: Double)

fun main() {
    val product = Product(1, "Laptop", 999.99)
    println(product)  // 出力: Product(id=1, name=Laptop, price=999.99)

    val updatedProduct = product.copy(price = 899.99)
    println(updatedProduct)  // 出力: Product(id=1, name=Laptop, price=899.99)

    val (id, name, price) = product
    println("ID: $id, Name: $name, Price: $price")
}

val pair = Pair("John", 25)
println("Name: ${pair.first}, Age: ${pair.second}")

Name: John, Age: 25

val (name, age) = Pair("Alice", 30)
println("Name: $name, Age: $age")

Name: Alice, Age: 30

val triple = Triple("Laptop", 999.99, 2)
println("Product: ${triple.first}, Price: ${triple.second}, Quantity: ${triple.third}")

Product: Laptop, Price: 999.99, Quantity: 2

val (product, price, quantity) = Triple("Tablet", 499.99, 5)
println("Product: $product, Price: $price, Quantity: $quantity")

Product: Tablet, Price: 499.99, Quantity: 5

fun getUserInfo(): Pair<String, Int> {
    return Pair("Bob", 28)
}

val userInfo = getUserInfo()
println("Name: ${userInfo.first}, Age: ${userInfo.second}")

class User(val name: String, val age: Int, val isActive: Boolean) {
    fun getUserInfo(): String {
        return "Name: $name, Age: $age, Active: $isActive"
    }
}

fun main() {
    val user = User("Alice", 30, true)
    println(user.getUserInfo())
}

Name: Alice, Age: 30, Active: true

class Product(val name: String, val price: Double = 0.0, val quantity: Int = 1)

fun main() {
    val defaultProduct = Product("Unknown")
    val specificProduct = Product("Laptop", 999.99, 2)

    println("Default Product: ${defaultProduct.name}, Price: ${defaultProduct.price}, Quantity: ${defaultProduct.quantity}")
    println("Specific Product: ${specificProduct.name}, Price: ${specificProduct.price}, Quantity: ${specificProduct.quantity}")
}

Default Product: Unknown, Price: 0.0, Quantity: 1
Specific Product: Laptop, Price: 999.99, Quantity: 2

class Rectangle(val width: Double, val height: Double) {
    fun area(): Double {
        return width * height
    }

    fun perimeter(): Double {
        return 2 * (width + height)
    }
}

fun main() {
    val rectangle = Rectangle(5.0, 3.0)
    println("Area: ${rectangle.area()}")
    println("Perimeter: ${rectangle.perimeter()}")
}

Area: 15.0
Perimeter: 16.0

open class Animal(val name: String) {
    open fun sound() {
        println("$name makes a sound.")
    }
}

class Dog(name: String) : Animal(name) {
    override fun sound() {
        println("$name barks.")
    }
}

fun main() {
    val dog = Dog("Rex")
    dog.sound()
}

Rex barks.

val mixedList: List<Any> = listOf("Alice", 25, 89.5, true)
println(mixedList)

[Alice, 25, 89.5, true]

data class User(val name: String, val age: Int, val isActive: Boolean)

fun main() {
    val users = listOf(
        User("Alice", 25, true),
        User("Bob", 30, false),
        User("Charlie", 28, true)
    )

    for (user in users) {
        println("${user.name}, ${user.age}, Active: ${user.isActive}")
    }
}

Alice, 25, Active: true  
Bob, 30, Active: false  
Charlie, 28, Active: true  

val userMap: Map<String, Any> = mapOf(
    "name" to "Alice",
    "age" to 25,
    "isActive" to true
)

println(userMap)

{name=Alice, age=25, isActive=true}

val mutableUserMap = mutableMapOf<String, Any>(
    "name" to "Bob",
    "age" to 30
)

mutableUserMap["isActive"] = false
mutableUserMap["city"] = "New York"

println(mutableUserMap)

{name=Bob, age=30, isActive=false, city=New York}

val users = listOf(
    mapOf("name" to "Alice", "age" to 25, "isActive" to true),
    mapOf("name" to "Bob", "age" to 30, "isActive" to false),
    mapOf("name" to "Charlie", "age" to 28, "isActive" to true)
)

for (user in users) {
    println("Name: ${user["name"]}, Age: ${user["age"]}, Active: ${user["isActive"]}")
}

Name: Alice, Age: 25, Active: true  
Name: Bob, Age: 30, Active: false  
Name: Charlie, Age: 28, Active: true  

sealed class Result {
    data class Success(val data: String) : Result()
    data class Error(val message: String) : Result()
    object Loading : Result()
}

fun handleResult(result: Result) {
    when (result) {
        is Result.Success -> println("Success: ${result.data}")
        is Result.Error -> println("Error: ${result.message}")
        is Result.Loading -> println("Loading...")
    }
}

fun main() {
    val success = Result.Success("Data loaded successfully")
    val error = Result.Error("Network error")
    val loading = Result.Loading

    handleResult(success)  // 出力: Success: Data loaded successfully
    handleResult(error)    // 出力: Error: Network error
    handleResult(loading)  // 出力: Loading...
}

sealed interface Animal {
    fun sound()
}

class Dog : Animal {
    override fun sound() = println("Bark")
}

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

fun handleAnimal(animal: Animal) {
    when (animal) {
        is Dog -> animal.sound()
        is Cat -> animal.sound()
    }
}

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

    handleAnimal(dog)  // 出力: Bark
    handleAnimal(cat)  // 出力: Meow
}

import java.time.LocalDate

enum class Priority {
    HIGH, MEDIUM, LOW
}

data class Task(
    val title: String,
    val description: String,
    val dueDate: LocalDate,
    val priority: Priority,
    var isCompleted: Boolean = false
)

fun main() {
    val tasks = mutableListOf(
        Task("Learn Kotlin", "Complete the Kotlin basics tutorial", LocalDate.of(2024, 7, 15), Priority.HIGH),
        Task("Grocery Shopping", "Buy vegetables and fruits", LocalDate.of(2024, 7, 10), Priority.MEDIUM),
        Task("Workout", "Morning exercise for 30 minutes", LocalDate.of(2024, 7, 12), Priority.LOW)
    )

    // タスクの一覧を表示
    println("All Tasks:")
    for (task in tasks) {
        println(task)
    }
}

fun markTaskAsCompleted(tasks: MutableList<Task>, title: String) {
    val task = tasks.find { it.title == title }
    if (task != null) {
        task.isCompleted = true
        println("Task '${task.title}' marked as completed.")
    } else {
        println("Task with title '$title' not found.")
    }
}

fun main() {
    val tasks = mutableListOf(
        Task("Learn Kotlin", "Complete the Kotlin basics tutorial", LocalDate.of(2024, 7, 15), Priority.HIGH),
        Task("Grocery Shopping", "Buy vegetables and fruits", LocalDate.of(2024, 7, 10), Priority.MEDIUM)
    )

    markTaskAsCompleted(tasks, "Learn Kotlin")

    // タスクの状態を表示
    println("\nUpdated Tasks:")
    for (task in tasks) {
        println(task)
    }
}

Task 'Learn Kotlin' marked as completed.

Updated Tasks:
Task(title=Learn Kotlin, description=Complete the Kotlin basics tutorial, dueDate=2024-07-15, priority=HIGH, isCompleted=true)
Task(title=Grocery Shopping, description=Buy vegetables and fruits, dueDate=2024-07-10, priority=MEDIUM, isCompleted=false)

fun filterAndSortTasks(tasks: List<Task>) {
    val highPriorityTasks = tasks.filter { it.priority == Priority.HIGH }
    val completedTasks = tasks.filter { it.isCompleted }

    println("\nHigh Priority Tasks:")
    highPriorityTasks.forEach { println(it) }

    println("\nCompleted Tasks:")
    completedTasks.forEach { println(it) }
}

fun main() {
    val tasks = listOf(
        Task("Learn Kotlin", "Complete the Kotlin basics tutorial", LocalDate.of(2024, 7, 15), Priority.HIGH, true),
        Task("Grocery Shopping", "Buy vegetables and fruits", LocalDate.of(2024, 7, 10), Priority.MEDIUM),
        Task("Workout", "Morning exercise for 30 minutes", LocalDate.of(2024, 7, 12), Priority.LOW, true)
    )

    filterAndSortTasks(tasks)
}

High Priority Tasks:
Task(title=Learn Kotlin, description=Complete the Kotlin basics tutorial, dueDate=2024-07-15, priority=HIGH, isCompleted=true)

Completed Tasks:
Task(title=Learn Kotlin, description=Complete the Kotlin basics tutorial, dueDate=2024-07-15, priority=HIGH, isCompleted=true)
Task(title=Workout, description=Morning exercise for 30 minutes, dueDate=2024-07-12, priority=LOW, isCompleted=true)

val age: Int = "25"  // String型をInt型に代入

Type mismatch: inferred type is String but Int was expected

val age: Int = "25".toInt()

val name: String = null  // Nullを非Null型に代入

Null can not be a value of a non-null type String

val name: String? = null  // Null許容型
val defaultName: String = "Unknown"  // デフォルト値を設定

val list = listOf("Alice", "Bob")
println(list[2])  // インデックス2は存在しない

java.lang.IndexOutOfBoundsException: Index 2 out of bounds for length 2

println(list.getOrNull(2) ?: "Index out of bounds")

sealed class Result
class Success : Result()
class Error : Result()

fun handleResult(result: Result) {
    when (result) {
        is Success -> println("Success")
        // Errorクラスの処理がない
    }
}

'when' expression must be exhaustive

fun handleResult(result: Result) {
    when (result) {
        is Success -> println("Success")
        is Error -> println("Error")
    }
}

data class User(val name: String, val age: Int)

val user = User("Alice", 25)
val updatedUser = user.copy(age = "30")  // Int型にString型を渡している

Type mismatch: inferred type is String but Int was expected

val updatedUser = user.copy(age = 30)