How to set not null for function params in kotlin

Question

I'm creating one function in Kotlin. It validates email and password fields. I want to apply email and password should not be null. @NotNull kinda annotation here.

Does anyone know how to do this in Kotlin? So the caller cannot send the null value.

private fun isEmailAndPasswordValid(email: String, password: String): Boolean {

    if (email.isEmpty()) return false

    if (!Patterns.EMAIL_ADDRESS.matcher(email).matches()) return false

    if (password.isEmpty()) return false

    return true
}

Answer 1

Kotlin differentiates all types by nullable and not-nullable. For example, the class String can be used for the type String, which is not nullable, and the type String?, which IS nullable, i.e. could hold null.

In your example no nullable types are used, so you’re all good - no additional annotation needed.

The documentation should be studied for further information.

Answer 2

The Kotlin language is by default null-safe so when creating a new variable it can't be null, but when you want a nullable variable you can add The exclamation mark to specify that it can be null for Example String?, Int? ...

Not Nullable

var a: String = "bachiri"
a = null // compilation error

Nullable Type

var a: String? = "bachiri"
a = null // OK

and bare in mind if you want to call a function on the nullable Type you should use eighter the check for null variable(1) or use the safe calls(2)