Kotlin Tip #24: Use lateinit for Late Initialization of Non-null Variables — 100 Kotlin Tips in 100 Days
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Tip #23: Use type aliases to provide alternative names for existing types
One of the Kotlin language’s core principles is its emphasis on null safety, aiming to eliminate the dreaded NullPointerException from your code. However, there are scenarios where you cannot initialize a variable at the point of declaration but are confident it will be initialized before use. For these cases, we can use thelateinit keyword.
The lateinit modifier allows you to declare non-null properties without immediately initializing them, providing a promise that they will be initialized before any operations are performed on them. This feature is particularly useful for dependency injection, unit testing, or initializing variables that depend on some configuration not available at the object's construction time.
You declare a lateinit variable by placing the lateinit keyword before the variable type. Note that lateinit can only be used with mutable variables (var) and with types that are non-nullable and not primitive.
class MyClass {
lateinit var dependency: SomeDependencyClass
}Consider a scenario where you have a class that requires a context or configuration to initialize its properties. With lateinit, you can simplify the initialization process:
In the above example, userConfig is a non-null, uninitialized property. It gets initialized through the initializeWithConfig method.
However, bear in mind that if you try to access the property before initialization, you will get a UninitializedPropertyAccessException.
That's why The processUser method checks if userConfig is initialized, ensuring the class is used correctly.
lateinit is a testament to Kotlin's flexibility, offering a balance between null safety and practical usability. It simplifies handling late-initialized properties while keeping the code safe and concise.
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Tip #25: Use
check()for precondition validation in your code
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