Initializing lazy and lateinit variables in Kotlin


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Kotlin commonly demands us to initialize attributes as soon as we determine them. Carrying out this appears odd when we don’t know the excellent original value, in particular in the case of lifecycle-pushed Android houses.

Luckily for us, there is a way to get through this difficulty. The IntelliJ Notion editor will alert you if you declare a course residence without the need of initializing it and recommend introducing a lateinit search term.

What if an initialized assets or object does not in fact get used in the program? Well, these unused initializations will be liabilities to the method since item development is a significant procedure. This is yet another case in point of in which lateinit can appear to our rescue.

This write-up will clarify how the lateinit modifier and lazy delegation can consider care of unused or pointless early initializations. This will make your Kotlin progress workflow more economical completely.

lateinit in Kotlin

The lateinit search term stands for “late initialization.” When applied with a class assets, the lateinit modifier keeps the home from being initialized at the time of its class’ item design.

Memory is allocated to lateinit variables only when they are initialized later in the software, fairly than when they are declared. This is pretty convenient in conditions of adaptability in initialization.

Let us appear at some vital functions that lateinit has to provide!

Key options

For starters, memory is not allocated to a lateinit assets at the time of declaration. The initialization usually takes spot later on when you see match.

A lateinit home may modify more than at the time through the program and is intended to be mutable. That’s why you ought to generally declare it as a var and not as a val or const.

The lateinit initialization can conserve you from repetitive null checks that you may want when initializing homes as nullable varieties. This attribute of lateinit properties does not assist the nullable form.

Increasing on my final level, lateinit can be utilised properly with non-primitive facts kinds. It doesn’t get the job done with primitive types like extended or int. This is for the reason that each time a lateinit residence is accessed, Kotlin delivers it a null worth beneath the hood to indicate that the assets has not been initialized nonetheless.

Primitive types just cannot be null, so there is no way to suggest an uninitialized home. In consequence, primitive forms toss an exception when utilised with the lateinit key word.

Lastly, a lateinit house will have to be initialized at some stage in advance of it is accessed or it will toss an UninitializedPropertyAccessException mistake, as found down below:

Uninitialized Property Access Exception Error

A lateinit residence accessed in advance of initialization sales opportunities to this exception.

Kotlin will allow you to look at if a lateinit residence is initialized. This can be useful to offer with the uninitialization exception we just discussed.

lateinit var myLateInitVar: String

  // Do anything

Illustrations of the lateinit modifier in use

Let’s see the lateinit modifier in action with a very simple example. The code under defines a course and initializes some of its homes with dummy and null values.

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course TwoRandomFruits 
  var fruit1: String = "tomato" 
  var fruit2: String? = null

  enjoyable randomizeMyFruits() 
      fruit1 = randomFruits()
      fruit2 = possiblyNullRandomFruits()

  enjoyable randomFruits(): String  ... 
  exciting possiblyNullRandomFruits(): String?  ... 

enjoyable main() 
    val rf= RandomFruits()

    println(rf.fruit2?.capitalize()) // Null-test

This is not the very best way to initialize a variable, but in this scenario, it even now does the job.

As you can see over, if you opt for to make the property nullable, you’ll have to null check out it whenever you modify or use it. This can be instead tiresome and aggravating.

Let’s tackle this difficulty with the lateinit modifier:

course TwoRandomFruits 
  lateinit var fruit1: String // No preliminary dummy worth needed
  lateinit var fruit2: String // Nullable kind is not supported right here

  enjoyable randomizeMyFruits() 
      fruit1 = randomFruits()
      fruit2 = when 
          possiblyNullRandomFruits() == null -> "Tomato" // Dealing with null values
          else -> possiblyNullRandomFruits()!!

  exciting randomFruits(): String  ... 
  exciting possiblyNullRandomFruits(): String?  ... 

enjoyment principal() 
    val rf= RandomFruits()


You can see this code in motion in this article.

The lateinit implementation speaks for itself and demonstrates a neat way to deal with variables! Aside from the default conduct of lateinit, the main takeaway listed here is how very easily we can stay clear of working with the nullable variety.

Lifecycle-driven properties and lateinit

Knowledge binding is one more example of making use of lateinit to initialize an activity later on. Builders frequently want to initialize the binding variable before to use it as a reference in other approaches for accessing various sights.

In the MainActivity course under, we declared the binding with the lateinit modifier to obtain the exact same issue.

package deal com.take a look at.lateinit

import ...

course MainActivity : AppCompatActivity() 
  lateinit var binding: ActivityMainBinding

  override entertaining onCreate(savedInstanceState: Bundle?) 
    binding = DataBindingUtil.setContentView(this, R.layout.activity_most important)


The binding for MainActivity can only get initialized when the action lifecycle purpose, onCreate(), gets fired. Hence, declaring the binding with the lateinit modifier would make total sense here.

When to use lateinit

With common variable initialization, you have to incorporate a dummy and, most probably, a null worth. This will incorporate a good deal of null checks when they are accessed.

// Standard initialization
var identify: String? = null
name = getDataFromSomeAPI()
// A null-examine will be demanded when `name` is accessed.
name?.permit  it-> 

// Lateinit initialization
lateinit var name: String
title = getDatafromSomeAPI()

We can use the lateinit modifier to keep away from these repeated null checks, specially when a residence is probable to fluctuate regularly.

Points to bear in mind when using lateinit

It’s great to remember to usually initialize a lateinit assets ahead of accessing it, or else, you will see a significant exception thrown at the time of compilation.

Make sure to also hold the property mutable by working with a var declaration. Applying val and const won’t make any feeling, as they show immutable properties with which lateinit will not function.

Ultimately, stay away from making use of lateinit when the given property’s knowledge style is primitive or the chances of a null value are high. It is not created for these scenarios and doesn’t support primitive or nullable styles.

Lazy delegation in Kotlin

As the title indicates, lazy in Kotlin initializes a residence in a lazy manner. Fundamentally, it creates a reference but only goes for the initialization when the home is utilised or called for the first time.

Now, you may well be asking how this is diverse from common initialization. Perfectly, at the time of a class object development, all of its public and non-public properties get initialized inside its constructor. There is some overhead affiliated with initializing variables in a course the much more variables, the better the overhead will be.

Let us realize it with an instance:

course X 
  enjoyment doThis() 

class Y 
  val shouldIdoThis: Boolean = SomeAPI.information()
  val x = X()


Even with not utilizing it, course Y in the previously mentioned code even now has an object established of course X. Class X will also gradual down Y if it is a closely built class.

Avoidable object development is inefficient and may possibly sluggish down the latest class. It could be that some houses or objects are not needed below specified ailments, based on the application movement.

It could also be that qualities or objects rely on other houses or objects for creation. Lazy delegation offers with these two possibilities successfully.

Important features

A variable with lazy initialization will not be initialized until eventually it’s identified as or utilised. This way, the variable is initialized only at the time and then its benefit is cached for further use in the system.

Considering the fact that a residence initialized with lazy delegation is intended to use the exact same value all over, it is immutable in character and is normally employed for read-only homes. You need to mark it with a val declaration.

It is thread-harmless, i.e. computed only once and shared by all threads by default. When initialized, it remembers or caches the initialized worth in the course of the application.

In distinction to lateinit, lazy delegation supports a customized setter and getter that permits it to accomplish intermediate functions though reading and producing the price.

Case in point of lazy delegation in use

The code beneath implements very simple math to compute the areas of selected designs. In the situation of a circle, the calculation would require a frequent worth for pi.

course Place 
  val pi: Float = 3.14f

  enjoyable circle(radius: Int): Float = pi * radius * radius
  fun rectangle(duration: Int, breadth: Int = length): Int = length * breadth
  enjoyment triangle(foundation: Int, top: Int): Float = base * top * .5f

entertaining most important() 
  val space = Space()
  val squareSideLength = 51

  println("Space of our rectangle is $region.rectangle(squareSideLength)")

As you can see above, no calculation of the spot of any circle was concluded, building our definition of pi useless. The home pi however will get initialized and allocated memory.

Let us rectify this problem with the lazy delegation:

class Area 
  val pi: Float by lazy 

  exciting circle(...) = ...
  entertaining rectangle(...) = ...
  pleasurable triangle(...) = ...

enjoyable main() 
  val region = Region()
  val squareSideLength = 51
  val circleRadius = 37

  println("Location of our rectangle is $location.rectangle(squareSideLength)")
  println("Spot of our circle is $")

You can see a demo of the over example here.

The earlier mentioned implementation of lazy delegation tends to make use of pi only when it is accessed. After accessed, its price is cached and reserved to use all through the system. We’ll see it in action with objects in the following examples.

Intermediate steps

Here’s how you can incorporate some intermediate steps even though producing values by way of lazy delegation. The below code lazy initializes a TextView in an Android activity.

Each time this TextView gets referred to as for the initially time inside of the MainActivity, a debug message with a LazyInit tag will be logged, as proven down below in the lambda purpose of the delegate:

class MainActivity : AppCompatActivity() 
  override fun onCreate(...) 
    val sampleTextView: TextView by lazy 
      Log.d("LazyInit", "sampleTextView")

Lazy delegation in Android apps

Now let’s transfer on to the application of lazy delegation in Android apps. The most basic use scenario can be our past illustration of an Android action that utilizes and manipulates a view conditionally.

deal com.examination.lazy

import androidx.appcompat.application.AppCompatActivity
import ...

class MainActivity : AppCompatActivity() {
  lateinit var binding: ActivityMainBinding

  override enjoyment onCreate(savedInstanceState: Bundle?) 
    binding = DataBindingUtil.setContentView(this, R.layout.action_primary)

    val sharedPrefs by lazy 

    val startButton by lazy 

    if(sharedPrefs.getBoolean("firstUse", genuine)) 
      startButton.isVisible = real
        // End onboarding, move to primary monitor some thing like that
        sharedPrefs.setBoolean("firstUse", false)


Previously mentioned, we initialized the SharedPreferences and a Button with lazy delegation. The logic entails the implementation of an onboarding display centered on a boolean price fetched from shared preferences.

The variation in between by lazy and = lazy

The by lazy statement provides an improvement by the lazy delegate immediately to a provided property. Its initialization will come about only once upon its initial obtain.

val prop by lazy 

On the other hand, the = lazy statement retains a reference to the delegate object in its place, by which you may perhaps use the isInitialized() delegation strategy or access it with the worth assets.

val prop = lazy 



You can see a quick demo of the over code here.

When to use lazy

Consider making use of lazy delegates to lighten a course that will involve numerous and/or conditional creations of other course objects. If the object generation is dependent on an internal assets of the course, lazy delegation is the way to go.

course Personnel 
    enjoyable showDetails(id: Int): Checklist 
        val employeeRecords by lazy 
            EmployeeRecords(id) // Object's dependency on an interior home

Items to try to remember when applying lazy

Lazy initialization is a delegation that initializes one thing only when and only when it’s identified as. It’s meant to stay away from needless object development.

The delegate object caches the benefit returned on initially obtain. This cached price is employed even further in the application when required.

You may well get advantage of its customized getter and setter for intermediate steps when examining and composing values. I also favor applying it with immutable types, as I sense it is effective finest with values that stay unchanged during the software.


In this report, we talked about Kotlin’s lateinit modifier and lazy delegation. We confirmed some standard illustrations demonstrating their makes use of and also talked about some sensible use instances in Android development.

Thank you for having the time to examine this starter by means of the close! I hope you’ll be equipped to use this tutorial to implement these two options in your application growth journey.

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