Nullable types with ? suffix in Kotlin - Mini Project: Build & Apply

Nullable types with ? suffix

📖 Scenario: Imagine you are creating a simple contact list app. Some contacts have phone numbers, but some do not. You want to store phone numbers in a way that allows missing numbers without causing errors.

🎯 Goal: Learn how to use nullable types with the ? suffix in Kotlin to safely handle values that might be missing.

📋 What You'll Learn

Create a variable with a nullable type using the ? suffix

Assign a value and null to the nullable variable

Use safe call operator ?. to access the nullable variable

Print the results to see how Kotlin handles nullable types

💡 Why This Matters

🌍 Real World

Nullable types help apps handle missing or optional data safely, like missing phone numbers in contacts.

💼 Career

Understanding nullable types is essential for Kotlin developers to avoid crashes and write safe, reliable code.

1

Create a nullable variable

Create a variable called phoneNumber of type String? and assign it the value "123-456-7890".

Kotlin

# Create a variable called phoneNumber of type String? and assign "123-456-7890"
# Your code here

Need a hint?

Use String? to make the variable nullable.

2

Assign null to the nullable variable

Change the value of phoneNumber to null.

Kotlin

var phoneNumber: String? = "123-456-7890"
# Assign null to phoneNumber
# Your code here

Need a hint?

Just assign null to the variable.

3

Use safe call operator to access nullable variable

Create a variable called length and assign it the length of phoneNumber using the safe call operator ?..

Kotlin

var phoneNumber: String? = "123-456-7890"
phoneNumber = null
# Create variable length using phoneNumber?.length
# Your code here

Need a hint?

Use ?. to safely get length without error if phoneNumber is null.

4

Print the length variable

Print the value of length using println.

Kotlin

var phoneNumber: String? = "123-456-7890"
phoneNumber = null
val length = phoneNumber?.length
# Print length
# Your code here

Need a hint?

Just print length to see the result.