How to Use Safe Call Operator in Kotlin for Null Safety

In Kotlin, use the ?. safe call operator to access a property or method of an object only if it is not null. This prevents null pointer exceptions by returning null instead of throwing an error when the object is null.

Syntax

The safe call operator ?. is placed between a nullable object and the property or method you want to access. If the object is null, the whole expression returns null instead of causing an error.

• object?.property - safely access a property
• object?.method() - safely call a method

kotlin

val name: String? = null
val length = name?.length

Output

length is null

Example

This example shows how to safely get the length of a nullable string using the safe call operator. If the string is null, the length will also be null without causing an error.

kotlin

fun main() {
    val name: String? = null
    val length = name?.length
    println("Length: $length")

    val anotherName: String? = "Kotlin"
    val anotherLength = anotherName?.length
    println("Length: $anotherLength")
}

Output

Length: null
Length: 6

Common Pitfalls

One common mistake is to forget that the result of a safe call is nullable, so you must handle the null case. Also, using ?. on a non-nullable type is unnecessary. Avoid chaining safe calls without handling nulls, which can lead to unexpected null results.

kotlin

fun main() {
    val name: String? = null
    // Wrong: assuming length is non-null
    // val length: Int = name?.length  // Error: Type mismatch

    // Right: declare length as nullable Int?
    val length: Int? = name?.length
    println(length) // prints null
}

Output

null

Quick Reference

Use this quick guide to remember how the safe call operator works:

Expression	Meaning	Result if object is null
object?.property	Access property if object not null	null
object?.method()	Call method if object not null	null
object?.property?.method()	Chain safe calls	null if any part is null
object!!.property	Force access, throws if null	Throws NullPointerException

Key Takeaways

Use ?. to safely access properties or methods on nullable objects without errors.

The result of a safe call is always nullable; handle null cases properly.

Avoid unnecessary safe calls on non-nullable types.

Chaining safe calls returns null if any part is null, preventing exceptions.

Use !! only when you are sure the object is not null to avoid crashes.