android - Kotlin - How to decide between "lateinit" and "nullable variable"?

Question

I am confuse for lateinit and nullable variable, which one to use for variable.

lateinit var c: String
var d: String? = null
c = "UserDefinedTarget"

// if not added initialisation for c than throws UninitializedPropertyAccessException
if (c == "UserDefinedTarget") {
    //do some stuff.
}
//not throws any exception whether d is initialise or not.
if(d == "UserDefinedTarget") {
     //do some stuff
}

Answer 1

A type that is nullable is just that, a thing that has a valid state that is null.

A non-nullable late init var represents something where null is an invalid state, but for some reason you can't populate it in the constructor.

Android Activities are a good example of a use of lateinit. Activities must have a no args constructor and their lifecycle only really starts with onCreate().