Why null safety is Kotlin's defining feature - See It in Action

Why null safety is Kotlin's defining feature

📖 Scenario: Imagine you are building a simple contact list app. Sometimes, a contact might not have a phone number saved. You want to make sure your app does not crash when it tries to use a missing phone number.

🎯 Goal: You will learn how Kotlin's null safety helps prevent errors by forcing you to handle missing (null) values safely.

📋 What You'll Learn

Create a variable that can hold a phone number or no number (null)

Create a variable that cannot hold null

Use safe call operator to access the phone number safely

Use the Elvis operator to provide a default message if the phone number is missing

Print the results to see how Kotlin handles null safety

💡 Why This Matters

🌍 Real World

Apps often deal with missing or optional data like phone numbers or emails. Kotlin's null safety helps avoid crashes by making you handle these cases explicitly.

💼 Career

Understanding null safety is essential for Kotlin developers to write safe, reliable apps and avoid common runtime errors.

1

Create a nullable phone number variable

Create a variable called phoneNumber of type String? and set it to null.

Kotlin

# Create a variable called phoneNumber of type String? and set it to null
// Your code here

Need a hint?

Use String? to allow the variable to hold null.

2

Create a non-nullable contact name variable

Create a variable called contactName of type String and set it to "Alice".

Kotlin

var phoneNumber: String? = null
# Create a variable called contactName of type String and set it to "Alice"
// Your code here

Need a hint?

Do not add ? after String because this variable cannot be null.

3

Use safe call and Elvis operator to handle null phone number

Create a variable called displayNumber that uses phoneNumber?.length to get the length safely, and if phoneNumber is null, use ?: to set displayNumber to "No number".

Kotlin

var phoneNumber: String? = null
var contactName: String = "Alice"
# Create displayNumber using safe call and Elvis operator
// Your code here

Need a hint?

Use ?. to safely access length and ?: to provide a default value.

4

Print the contact name and phone number info

Write a println statement to print "Contact: " plus contactName and " - Phone length: " plus displayNumber.

Kotlin

var phoneNumber: String? = null
var contactName: String = "Alice"
val displayNumber = phoneNumber?.length ?: "No number"
# Print contactName and displayNumber
// Your code here

Need a hint?

Use string templates with $contactName and $displayNumber inside println.