Properties | Kotlin

Class member variables can have a lateinit property. It signifies a non-null member variable that is not initialised in a constructor but will be initialised later. The initialisation can happen, for example, in unit test setup functions.

public class Test {
	lateinit var foo: Foo
	
	@SetUp fun setup() {
		foo = GetFoo()
	}
 
	@Test fun test() {
		foo.method()
	}
}

When a uninitialised lateinit variable is accessed, a special exception is thrown. We can also check if the variable has been initialised or not. In the above example, we can use Test::foo.isInitialized