Creating instances without new keyword in Kotlin - Practice Exercises

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Kotlin object instantiation without 'new'

What is the output of this Kotlin code that creates an instance without using the 'new' keyword?

Kotlin

class Person(val name: String) {
    fun greet() = "Hello, $name!"
}

fun main() {
    val p = Person("Anna")
    println(p.greet())
}

A Hello, Anna!

B Hello, null!

C Compilation error: 'new' keyword required

D Runtime error: Uninitialized property

💡 Hint

In Kotlin, you create instances by calling the class name like a function.

Kotlin does not use the 'new' keyword. You create an instance by calling the class constructor directly. Here, Person("Anna") creates an instance with name 'Anna'.

❓ Predict Output

intermediate

Creating data class instance without 'new' keyword

What will be the output of this Kotlin code snippet?

Kotlin

data class Point(val x: Int, val y: Int)

fun main() {
    val p = Point(5, 10)
    println("x=${p.x}, y=${p.y}")
}

A x=0, y=0

B x=5, y=10

C Compilation error: Missing 'new' keyword

D Runtime error: Uninitialized properties

💡 Hint

Data classes are instantiated like normal classes in Kotlin.

Kotlin creates instances by calling the constructor directly. Here, Point(5, 10) creates an instance with x=5 and y=10.

🔧 Debug

advanced

Why does this Kotlin code fail to compile?

Identify the reason this Kotlin code does not compile.

Kotlin

class Animal(val type: String)

fun main() {
    val a = new Animal("Dog")
    println(a.type)
}

A The class Animal is missing a constructor

B The println statement is incorrect

C The property 'type' is not initialized

D Kotlin does not use the 'new' keyword to create instances

💡 Hint

Check how Kotlin creates instances compared to Java.

Kotlin creates instances by calling the constructor directly without 'new'. Using 'new' causes a compilation error.

🧠 Conceptual

advanced

How does Kotlin create instances without 'new'?

Which statement best explains how Kotlin creates instances without using the 'new' keyword?

A Kotlin requires a factory method to create instances

B Kotlin uses a hidden 'new' keyword that is not visible in code

C Kotlin calls the constructor directly as a function without requiring 'new'

D Kotlin uses reflection to create instances at runtime

💡 Hint

Think about how you write code to create objects in Kotlin.

Kotlin simplifies instance creation by calling the constructor directly, so no 'new' keyword is needed.

❓ Predict Output

expert

Output of Kotlin companion object instance creation

What is the output of this Kotlin code that creates an instance using a companion object without 'new'?

Kotlin

class Logger private constructor(val level: String) {
    companion object {
        fun create(level: String) = Logger(level)
    }
}

fun main() {
    val log = Logger.create("DEBUG")
    println(log.level)
}

A DEBUG

B Compilation error: private constructor inaccessible

C null

D Runtime error: Cannot access companion object

💡 Hint

Companion objects can create instances even with private constructors.

The companion object method 'create' calls the private constructor internally, allowing instance creation without 'new'.