Sunday 17 May 2020

lateinit Vs by lazy

Both "lateinit" and "by lazy" are Kotlin Property initializers.

  • Use it with mutable variable [var]
  • Allowed with only non-nullable data types
  • This modifier is not allowed on properties of primitive types
  • It is a promise to compiler that the value will be initialized in future.
  • If you try to access lateinit variable without initializing it then it throws UnInitializedPropertyAccessException.
by lazy:
  • Lazy initialization was designed to prevent unnecessary initialization of objects.
  • Your variable will not be initialized unless you use it.
  • It is initialized only once. Next time when you use it, you get the value from the memory.
  • It is thread safe (It initializes in the thread where it is used for the first time. Other threads use the same value stored in the cache).
  • The variable can only be val.
  • The variable can only be non-nullable.
class Basic {
    private lateinit var strMsg: String
    private val strMsg1: String by lazy {
        println("Lazy Initializing - Variable born")
        return@lazy "Tester"

    fun initBasic() {
        //Late Initialization - Check
        println("strMsg initialization status is ${::strMsg.isInitialized}");
        strMsg = "Testing"
        println("strMsg value is $strMsg, now the initialization status is ${::strMsg.isInitialized}");

        //Lazy Initialization - Check
        println("strMsg1 value is ${strMsg1}");

fun main(ar: Array<String>) {

Console Output:

strMsg initialization status is false
strMsg value is Testing, now the initialization status is true
Lazy Initializing - Variable born
strMsg1 value is Tester