Safe casts with as? in Kotlin - Mini Project: Build & Apply

Safe casts with as? in Kotlin

📖 Scenario: Imagine you have a list of different types of objects, like numbers and words. You want to find out which ones are numbers and work with them safely without causing errors.

🎯 Goal: You will learn how to use the safe cast operator as? in Kotlin to convert objects to a specific type safely. This helps avoid crashes when the object is not of the expected type.

📋 What You'll Learn

Create a list called items with mixed types

Create a variable called countInts to count integers

Use a for loop with variables item to iterate over items

Use safe cast item as? Int inside the loop

Print the count of integers using print

💡 Why This Matters

🌍 Real World

Safe casts help when working with data from mixed sources, like user input or APIs, where types may vary.

💼 Career

Understanding safe casts is important for Kotlin developers to write robust and crash-free apps, especially in Android development.

1

Create a list with mixed types

Create a list called items with these exact values: 1, "hello", 3, "world", 5

Kotlin

# Create the list called items with 1, "hello", 3, "world", 5
# Your code here

Need a hint?

Use listOf() to create the list with the exact values.

2

Create a counter variable

Create a variable called countInts and set it to 0 to count how many integers are in the list

Kotlin

val items = listOf(1, "hello", 3, "world", 5)
# Create countInts variable and set it to 0
# Your code here

Need a hint?

Use var to create a variable that can change.

3

Use safe cast to count integers

Use a for loop with variable item to iterate over items. Inside the loop, use safe cast item as? Int to check if item is an integer. If it is, increase countInts by 1

Kotlin

val items = listOf(1, "hello", 3, "world", 5)
var countInts = 0
# Add a for loop to iterate over items
# Use safe cast item as? Int inside the loop
# Increase countInts if item is Int
# Your code here

Need a hint?

Use as? to safely cast and check for null before counting.

4

Print the count of integers

Write print(countInts) to display how many integers are in the list

Kotlin

val items = listOf(1, "hello", 3, "world", 5)
var countInts = 0
for (item in items) {
    val number = item as? Int
    if (number != null) {
        countInts++
    }
}
# Print the countInts variable
# Your code here

Need a hint?

Use print() to show the final count.