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().

Answer 2

These are two completely different concepts.

You can use lateinit to avoid null checks when referencing the property. It's very convenient in case your properties are initialized through dependency injection, or, for example, in the setup method of a unit test.

However, you should keep in mind that accessing a lateinit property before it has been initialized throws an exception. That means you should use them only if you are absolutely sure, they will be initialized.

Nullable types, on the other hand, are used when a variable can hold null.

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class A {     lateinit var a: String      fun cat() {         print(a.length)  // UninitializedPropertyAccessException is thrown         a = "cat"         print(a.length)  // >>> 3     } }  class B {     var b: String? = null      fun dog() {         print(b.length)  // won't compile, null check is obligatory here         print(b?.length) // >>> null         b = "dog"         print(b?.length) // >>> 3     } } 

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For more information:

• Late-initialized properties
• Nullable types