Safely accessing lateinit properties in Kotlin

Kotlin, by design, doesn’t allow a non-null variable to be left uninitialized during it’s declaration. Whenever you declare a lateinit var, you need to initialize it before you access it. Otherwise, you’ll be greeted with a fancy exception like this:

Exception in thread "main" kotlin.UninitializedPropertyAccessException: lateinit property fullName has not been initialized
	at UninitializedPropertyKt.main(UninitializedProperty.kt:3)

Don’t mistake this for a puny exception. It’ll crash your app. So, how to solve this problem?

Taking the rookie approach

The most lucrative solution to this problem would be to make the property a regular nullable one instead of a lateinit var and assign a value later on. You can do something like this:

var fullName: String? = null

And then just do a plain null check or kotlin null-check operator ? whenever you’re accessing the value.

if (fullName != null) {
    print("Hi, $fullName")
var length = fullName?.length ?: 0

Kind of like Java. But hang on a sec, Kotlin is supposed to be better than Java. Also, one of the USPs of Kotlin was eliminating the fiasco caused by a NullPointerException.

So, why go the traditional route?

Here’s a better solution.

Going the Kotlinish way

If you’re using Kotlin 1.2, you can easily check whether a lateinit variable has been initialized or not. If not, well, you can always use the not null approach.

Anyways, here’s how you can check if a lateinit var has been initialized or not:

if (::fullName.isInitialized) {
    print("Hi, $fullName")

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Wajahat Karim
🌍 Making the world a better place, one app at a time.
🔥 Google Developer Expert (GDE) in Android . 📱 Professional Android Developer with ~10 years experience. 💻 Creator of various Open Source libraries on Android . 📝 Author of two technical books and 100+ articles on Android. 🎤 A passionate Public Speaker giving talks all over the world.
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Wajahat Karim

🔥 Google Dev Expert (GDE) in Android .
📱 Android Dev. 💻 Open Source Contributor . 📝 Technical Writer . 🎤 Public Speaker

Senior Android Developer

Karachi, Pakistan