Exercise: User Information Processor

Implement the processUserInformation function according to the following rules:

• If the input user is null, return "Missing user information".
• If name from user is null, throw an IllegalArgumentException.
• If age from user is null, treat it as 0.
• If email from user is null or contains a blank email address, return "Missing email".
• Otherwise, return information about user in the following format: "User {name} is {age} years old, email: {email}".

Starting code:

fun processUserInformation(user: User?): String {
    return ""
}

data class EmailAddress(val email: String?)

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

Example usage:

println(processUserInformation(null))
// Missing user information

val user1 = User(
    "John",
    30,
    EmailAddress("[email protected]")
)
println(processUserInformation(user1))
// User John is 30 years old, email: [email protected]

val user2 = User(
    "Alice",
    null,
    EmailAddress("[email protected]")
)
println(processUserInformation(user2))
// User Alice is 0 years old, email: [email protected]

val user3 = User(
    "Bob",
    25,
    EmailAddress("") // or EmailAddress(null) or null
)
println(processUserInformation(user3))
// Missing email

val user6 = User(
    null,
    40,
    EmailAddress("[email protected]")
)
println(processUserInformation(user6))
// IllegalArgumentException

This problem can either be solved in the below playground or you can clone kotlin-exercises project and solve it locally. In the project, you can find code template for this exercise in essentials/nullability/UserInformation.kt. You can find there starting code, example usage and unit tests.

Once you are done with the exercise, you can check your solution here.

Playground

import org.junit.Assert.assertThrows
import org.junit.Test
import kotlin.test.assertEquals

fun processUserInformation(user: User?): String {
    return ""
}

data class EmailAddress(val email: String?)

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

fun main() {
    println(processUserInformation(null))
    // Missing user information
    
    val user1 = User(
        "John",
        30,
        EmailAddress("[email protected]")
    )
    println(processUserInformation(user1))
    // User John is 30 years old, email: [email protected]
    
    val user2 = User(
        "Alice",
        null,
        EmailAddress("[email protected]")
    )
    println(processUserInformation(user2))
    // User Alice is 0 years old, email: [email protected]
    
    val user3 = User(
        "Bob",
        25,
        EmailAddress("") // or EmailAddress(null) or null
    )
    println(processUserInformation(user3))
    // Missing email
    
    val user6 = User(
        null,
        40,
        EmailAddress("[email protected]")
    )
    println(processUserInformation(user6))
    // IllegalArgumentException
}

class StudentInformationTest {

    @Test
    fun `valid user information`() {
        val user = User("John Doe", 30, EmailAddress("[email protected]"))
        val result = processUserInformation(user)
        val expected = "User John Doe is 30 years old, email: [email protected]"
        assertEquals(expected, result)
    }

    @Test
    fun `null user information`() {
        val result = processUserInformation(null)
        val expected = "Missing user information"
        assertEquals(expected, result)
    }

    @Test
    fun `user with missing age should have age 0`() {
        val user = User("Alice", null, EmailAddress("[email protected]"))
        val result = processUserInformation(user)
        val expected = "User Alice is 0 years old, email: [email protected]"
        assertEquals(expected, result)
    }

    @Test
    fun `user with blank email`() {
        val user = User("Bob", 25, EmailAddress(""))
        val result = processUserInformation(user)
        val expected = "Missing email"
        assertEquals(expected, result)
    }

    @Test
    fun `user with null email address`() {
        val user = User("Bob", 25, EmailAddress(null))
        val result = processUserInformation(user)
        val expected = "Missing email"
        assertEquals(expected, result)
    }

    @Test
    fun `user with null email information`() {
        val user = User("Bob", 25, null)
        val result = processUserInformation(user)
        val expected = "Missing email"
        assertEquals(expected, result)
    }

    @Test
    fun `user with missing name should throw exception`() {
        val user = User(null, 40, EmailAddress("[email protected]"))
        assertThrows(IllegalArgumentException::class.java) {
            processUserInformation(user)
        }
    }
}