Lateinit and Lazy in Kotlin: A Guide to Optimal Property Initialization

Lateinit and Lazy in Kotlin: A Guide to Optimal Property Initialization

In the Kotlin realm, delayed property initialization is a common practice. Two keywords, lateinit and lazy, offer distinct approaches to achieve this. Understanding their nuances is crucial for crafting efficient and resilient code.

Let's dive into their characteristics, use cases, and best practices:

Understanding lateinit:

  • Defer initialization: Declare a property without initializing it immediately.

  • Guaranteed future initialization: You promise to initialize it before use.

  • Mutable properties (var) only.

  • Non-nullable: It trusts you to handle initialization responsibly.

  • Manual initialization: Assign a value before accessing it.

  • Runtime exception for uninitialized access: Be mindful of potential errors.


class MyActivity : Activity() {
    lateinit var myButton: Button  // Declared, but not initialized yet

    override fun onCreate(savedInstanceState: Bundle?) {

        myButton = findViewById(  // Initialization happens later
        myButton.setOnClickListener { /* do something */ }

Understanding lazy:

  • Initialize on first access: The property initializes only when it's first used.

  • Efficient memory usage: Resources are allocated only when needed.

  • Mutable or immutable properties (var or val).

  • Can be nullable or non-nullable: Offers flexibility.

  • Custom initialization block: Control the initialization process precisely.

  • Compile-time checks for initialization: Catches errors early, preventing runtime surprises.


class MyClass {
    val expensiveData by lazy {
        // Resource-intensive calculation happens only when accessed

Key Considerations:

  • Use lateinit when:

    • You need control over initialization timing.

    • You're confident the property will be initialized before access.

    • Examples: Injecting dependencies, accessing views within lifecycle-aware components.

  • Use lazy when:

    • You prioritize efficiency and resource management.

    • Initialization is expensive or might not always be necessary.

    • Examples: Loading data on demand, creating resource-intensive objects only when needed.


  • lateinit offers flexibility but requires careful handling to avoid runtime errors.

  • lazy provides safety and efficiency, but might introduce a slight delay on first access.

Experiment and explore: Apply these keywords in your own projects to experience their behavior firsthand.

By understanding lateinit and lazy, you’ll write more expressive, efficient, and robust Kotlin code. Choose wisely and create exceptional Kotlin experiences!