What is ‘lateinit’ Variable in Kotlin?

In Kotlin, you can declare a property or variable as 'lateinit' (short for “late initialization”) when you want to initialize a non-null value before you try to access it. This is particularly useful when working with dependency injection or when you’re certain that the variable will have a value set before it’s used, but you can’t initialize it immediately.

Related: How to check if ‘lateinit’ variable is initialized

1. Usage of lateinit Variable

In Kotlin, lateinit variables are used when you know that a property will be initialized before it is accessed, but you can’t initialize it immediately, For example:

  • When working with dependency injection
  • Certain Android app development scenarios.
  • Testing
  • Lazy initialization

lateinit allows you to defer the initialization until later in your code while ensuring that you won’t encounter null pointer exceptions when accessing the variable.

1.1 Syntax of lateinit Variable

Following is the syntax to declare lateinit variable.

Note that ‘lateinit‘ modifier is allowed only on mutable local variables like var. Hence, you cannot use for val variables.

1.2 Using lateinit Variable

Let’s create and use the lateinit variable in a simple example.

In this example, we simply created two lateinit variables name and city, later only name variable has been initialized with a non-null value Kumar. When we print name variable, it prints the associated value Kumar on the console. Printing city variable returns an exception UninitializedPropertyAccessException as it’s not initialized.

2. Handling Exception

So when you access lateinit variable without initializing, Kotlin returns an exception UninitializedPropertyAccessException with error message “lateinit property has not been initialized“. By using tr-catch you can handle this exception and take appropriate action.

Check lateinit Variable is Initialized

To check if a lateinit variable has been initialized in Kotlin, you can use the ::variableName.isInitialized syntax. This expression will return true if the lateinit variable initialized a non-null value, and false if it is not initialized.

The :: creates a member reference or a class reference.

In this example, the name variable is declared as a lateinit property of type String. This variable has been initialized in the initializeName() function. The ::name.isInitialized check is used to determine if the name property has been initialized to avoid a lateinit property access exception.

Alternatively, you can also use this::name.isInitialized


In this article, you have learned what is lateinit variable in Kotlin and how to declare, initialize a value, and access the variable. In summary

Naveen (NNK)

Naveen (NNK) is a Data Engineer with 20+ years of experience in transforming data into actionable insights. Over the years, He has honed his expertise in designing, implementing, and maintaining data pipelines with frameworks like Apache Spark, PySpark, Pandas, R, Hive and Machine Learning. Naveen journey in the field of data engineering has been a continuous learning, innovation, and a strong commitment to data integrity. In this blog, he shares his experiences with the data as he come across. Follow Naveen @ @ LinkedIn

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