Lazy evaluation vs eager evaluation in Kotlin - Hands-On Comparison

Lazy evaluation vs eager evaluation in Kotlin

📖 Scenario: Imagine you have a list of numbers and you want to find which numbers are even and then double them. You can do this in two ways: eagerly (all at once) or lazily (only when needed).

🎯 Goal: You will create a Kotlin program that shows the difference between eager and lazy evaluation by filtering and mapping a list of numbers.

📋 What You'll Learn

Create a list of integers called numbers with values 1 to 5

Create a variable called threshold set to 3

Use eager evaluation with filter and map on numbers to get doubled even numbers

Use lazy evaluation with asSequence(), filter, and map on numbers

Print both results to compare

💡 Why This Matters

🌍 Real World

Lazy evaluation helps improve performance by delaying work until it is really needed, useful in big data processing or UI updates.

💼 Career

Understanding lazy vs eager evaluation is important for writing efficient Kotlin code in Android apps and backend services.

1

Create the list of numbers

Create a list of integers called numbers with the exact values 1, 2, 3, 4, 5.

Kotlin

// Create the list called numbers with values 1 to 5
// Your code here

Need a hint?

Use listOf to create the list with the exact numbers.

2

Add a threshold variable

Create an integer variable called threshold and set it to 3.

Kotlin

val numbers = listOf(1, 2, 3, 4, 5)
// Create the threshold variable and set it to 3
// Your code here

Need a hint?

Just create a variable with val threshold = 3.

3

Apply eager evaluation

Create a variable called eagerResult that uses eager evaluation by calling filter on numbers to keep even numbers, then map to double them.

Kotlin

val numbers = listOf(1, 2, 3, 4, 5)
val threshold = 3
// Create eagerResult using filter and map eagerly
// Your code here

Need a hint?

Use filter { it % 2 == 0 } to get even numbers and map { it * 2 } to double them.

4

Apply lazy evaluation and print results

Create a variable called lazyResult that uses lazy evaluation by converting numbers to a sequence with asSequence(), then applying filter and map. Finally, print eagerResult and lazyResult converted to a list.

Kotlin

val numbers = listOf(1, 2, 3, 4, 5)
val threshold = 3
val eagerResult = numbers.filter { it % 2 == 0 }.map { it * 2 }
// Create lazyResult using asSequence, filter, and map
// Print eagerResult and lazyResult.toList()
// Your code here

Need a hint?

Use asSequence() on numbers, then filter and map. Print both results to see they match.