Kotlin's type system is advanced enough that it can track the difference between nullable types and non-nullable types. When we define a variable in Kotlin, as we have been doing so far, we cannot assign a null to it. This code, for instance, would not compile:
val name: String = null // does not compile
Assigning null to a var variable will not compile either:
var name: String = "harry"
name = null // does not compile
To inform the Kotlin compiler that we will allow a variable to contain a null, we must suffix the type with a ? operator:
var name: String? = "harry"
name = null
Both the preceding snippets will now compile.
Similarly, we can return nullable and non-nullable types from a function, use them as function parameters, and so on:
fun name1(): String = ...
fun name2(): String? = ...
The name1 function cannot...