Also function behavior and use cases in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code using also?

Consider the following Kotlin code snippet using the also function. What will be printed when this code runs?

Kotlin

val result = mutableListOf<Int>().also {
    it.add(1)
    it.add(2)
    it.add(3)
}
println(result)

A [1, 2, 3]

B []

C null

D Compilation error

💡 Hint

Remember that also returns the original object after applying the block.

The also function executes the block with the object as it and returns the original object. Here, elements are added to the list inside also, so result contains [1, 2, 3].

🧠 Conceptual

intermediate

What is the main purpose of the also function in Kotlin?

Choose the best description of what the also function is used for in Kotlin.

A To filter elements from a collection based on a condition.

B To perform additional actions on an object and return the original object.

C To transform an object and return the transformed result.

D To create a new object by copying an existing one.

💡 Hint

Think about whether also changes the object or just lets you do something with it.

also lets you run extra code using the object as it and then returns the original object unchanged. It is useful for side effects like logging or modifying the object.

🔧 Debug

advanced

Why does this Kotlin code using also cause a NullPointerException?

Examine the code below. Why does it throw a NullPointerException at runtime?

Kotlin

var name: String? = null
val result = name.also {
    println(it!!.length)
}
println(result)

A Because <code>also</code> returns null and println cannot print null.

B Because <code>println</code> cannot be called inside <code>also</code>.

C Because <code>also</code> cannot be called on nullable types.

D Because <code>it!!</code> forces a non-null assertion on a null value causing the exception.

💡 Hint

Check what it!! means when it is null.

The !! operator asserts that the value is not null. Since name is null, it!! throws a NullPointerException.

🚀 Application

advanced

How to use also to log and return an object in Kotlin?

You want to log the value of a variable while returning it unchanged in a Kotlin function. Which code snippet correctly uses also for this purpose?

A val x = compute().also { println("Value is $it") }

B val x = compute().apply { println("Value is $this") }

C val x = compute().run { println("Value is $this") }

D val x = compute().let { println("Value is $it") }

💡 Hint

also returns the original object after running the block with it.

also is perfect for logging because it runs the block with the object as it and returns the original object unchanged. let returns the block result, run returns the block result, and apply returns the object but uses this as receiver.

❓ Predict Output

expert

What is the output of this Kotlin code combining also and apply?

Analyze the code below. What will be printed when it runs?

Kotlin

data class Person(var name: String, var age: Int)

val person = Person("Alice", 25).also {
    println("Also: ${it.name}")
}.apply {
    age += 1
    println("Apply: $age")
}
println("Final: ${person.age}")

A

Also: Alice
Apply: 26
Final: 25

B

Also: Alice
Apply: 25
Final: 25

C

Also: Alice
Apply: 26
Final: 26

D

Also: Alice
Apply: 25
Final: 26

💡 Hint

Remember that apply runs with this and returns the object, also runs with it and returns the object.

also prints the name 'Alice'. apply increases age by 1 and prints 26. Finally, printing person.age shows 26 because the age was updated.