Kotlinでif文を使ったエラーメッセージの追加方法を詳しく解説

if (条件) {
    // 条件が真の場合に実行されるコード
} else {
    // 条件が偽の場合に実行されるコード
}

val number = 5
if (number > 0) {
    println("The number is positive.")
} else {
    println("The number is negative or zero.")
}

val number = -3
val message = if (number > 0) {
    "Positive"
} else {
    "Non-positive"
}
println(message) // 出力: Non-positive

val isAdult = true
if (isAdult) println("Access granted") else println("Access denied")

val userInput = ""
if (userInput.isEmpty()) {
    println("Error: Input cannot be empty.")
} else {
    println("Input is valid.")
}

val username = "John"
val password = ""
if (username.isEmpty() || password.isEmpty()) {
    println("Error: Username and password must not be empty.")
} else {
    println("Login successful.")
}

val number = -5
if (number < 0) {
    println("Error: The number cannot be negative.")
} else {
    println("The number is valid.")
}

val input = ""
if (input.isBlank()) {
    println("Error: Input must not be blank.")
} else {
    println("Input is accepted.")
}

val age = -1
if (age < 0) {
    println("Error: Age cannot be negative.")
} else if (age > 150) {
    println("Error: Age is not realistic.")
} else {
    println("Age is valid.")
}

if (条件1) {
    if (条件2) {
        // 条件1と条件2が真の場合の処理
    } else {
        // 条件1が真で条件2が偽の場合の処理
    }
} else {
    // 条件1が偽の場合の処理
}

val username = "John"
val password = ""

if (username.isEmpty()) {
    println("Error: Username cannot be empty.")
} else {
    if (password.isEmpty()) {
        println("Error: Password cannot be empty.")
    } else {
        println("Login successful.")
    }
}

val number = -4

if (number > 0) {
    if (number % 2 == 0) {
        println("The number is positive and even.")
    } else {
        println("The number is positive but not even.")
    }
} else {
    println("Error: The number is not positive.")
}

when (値) {
    条件1 -> 処理1
    条件2 -> 処理2
    else -> 処理3
}

val number = 0
val result = when {
    number > 0 -> "Positive"
    number < 0 -> "Negative"
    else -> "Zero"
}
println(result) // 出力: Zero

val input = "admin"
if (input == "admin") {
    println("Admin user")
} else if (input == "guest") {
    println("Guest user")
} else {
    println("Unknown user")
}

val input = "admin"
when (input) {
    "admin" -> println("Admin user")
    "guest" -> println("Guest user")
    else -> println("Unknown user")
}

val username = ""
val password = "123"

if (username.isBlank()) {
    println("Error: Username cannot be empty.")
} else if (password.length < 6) {
    println("Error: Password must be at least 6 characters long.")
} else {
    println("Login successful!")
}

val age = 20

when {
    age < 0 -> println("Error: Age cannot be negative.")
    age < 18 -> println("Error: You must be at least 18 years old.")
    else -> println("Welcome! Age is valid.")
}

val input: Any = 42

val message = when (input) {
    is String -> "Input is a String: $input"
    is Int -> if (input > 0) "Input is a positive Integer: $input" else "Error: Integer is not positive."
    else -> "Error: Unsupported input type."
}
println(message)

object ErrorMessages {
    const val EMPTY_USERNAME = "Error: Username cannot be empty."
    const val SHORT_PASSWORD = "Error: Password must be at least 6 characters long."
}

val username = ""
if (username.isBlank()) {
    println(ErrorMessages.EMPTY_USERNAME)
}

error.empty_username=Error: Username cannot be empty.
error.short_password=Error: Password must be at least 6 characters long.

import java.util.*

val messages = ResourceBundle.getBundle("messages")
println(messages.getString("error.empty_username"))

fun generateErrorMessage(field: String): String {
    return "Error: $field cannot be empty."
}

val username = ""
if (username.isBlank()) {
    println(generateErrorMessage("Username"))
}

data class ValidationError(val code: String, val message: String)

val errors = listOf(
    ValidationError("EMPTY_USERNAME", "Error: Username cannot be empty."),
    ValidationError("SHORT_PASSWORD", "Error: Password must be at least 6 characters long.")
)

val username = ""
if (username.isBlank()) {
    val error = errors.find { it.code == "EMPTY_USERNAME" }
    println(error?.message)
}

import org.junit.Assert.assertEquals
import org.junit.Test

class ErrorMessageTest {

    @Test
    fun testEmptyUsernameMessage() {
        val username = ""
        val errorMessage = if (username.isBlank()) {
            "Error: Username cannot be empty."
        } else {
            ""
        }
        assertEquals("Error: Username cannot be empty.", errorMessage)
    }
}

fun generateErrorMessage(field: String): String {
    return "Error: $field cannot be empty."
}

class ErrorMessageTest {

    @Test
    fun testDynamicMessage() {
        val expectedMessage = "Error: Username cannot be empty."
        val actualMessage = generateErrorMessage("Username")
        assertEquals(expectedMessage, actualMessage)
    }
}

import org.junit.Assert.assertEquals
import java.util.*

class ResourceMessageTest {

    @Test
    fun testResourceMessage() {
        val messages = ResourceBundle.getBundle("messages")
        val expectedMessage = "Error: Username cannot be empty."
        val actualMessage = messages.getString("error.empty_username")
        assertEquals(expectedMessage, actualMessage)
    }
}

class MultiConditionTest {

    @Test
    fun testMultipleConditions() {
        val username = ""
        val password = "123"

        val errorMessage = when {
            username.isBlank() -> "Error: Username cannot be empty."
            password.length < 6 -> "Error: Password must be at least 6 characters long."
            else -> "All inputs are valid."
        }

        assertEquals("Error: Username cannot be empty.", errorMessage)
    }
}