Kotlin Academy · Lesson

!! Operator: When and Why to Avoid It

Understand the non-null assertion operator, its risks, and better alternatives.

What Is !!?

The non-null assertion operator !! converts a nullable type to non-null. If the value is null at runtime, it throws NullPointerException.

x!! returns x if non-null, otherwise throws NPE.

fun main() {
    val name: String? = "Kotlin"
    val len: Int = name!!.length // 6
    println(len)
}