Elvis operator deep usage in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Elvis operator in Kotlin?

The Elvis operator (?:) in Kotlin is a shorthand to provide a default value when an expression is null. It returns the left side if it's not null, otherwise the right side.

beginner

How does the Elvis operator help with null safety?

It lets you handle nullable values concisely by providing a fallback value, avoiding explicit null checks and preventing null pointer exceptions.

intermediate

Explain chaining Elvis operators with an example.

You can chain Elvis operators to check multiple nullable values in order. For example: val result = a ?: b ?: c ?: "default". It returns the first non-null value among a, b, c, or "default" if all are null.

intermediate

How can the Elvis operator be used with function calls?

You can use it to call a function on a nullable object or provide a default if null. Example: val length = name?.length ?: 0 returns the length if name is not null, else 0.

advanced

What happens if you use the Elvis operator with a throw expression?

You can throw an exception as the right side of the Elvis operator to enforce non-null values. Example: val value = nullableValue ?: throw IllegalArgumentException("Value required") stops execution if nullableValue is null.

What does the Elvis operator ?: return if the left side is not null?

A Null

B The right side value

C The left side value

D Throws an exception

The Elvis operator returns the left side if it is not null; otherwise, it returns the right side.

Which of the following is a valid use of the Elvis operator?

A val result = a && b ?: c

B val result = a ?: b ?: "default"

C val result = a ? b : c

D val result = a +: b

Chaining Elvis operators like a ?: b ?: "default" is valid Kotlin syntax to provide fallback values.

What is the output of this code? val name: String? = null; val length = name?.length ?: 0; println(length)

A Length of name

B null

C Throws NullPointerException

D 0

Since name is null, name?.length is null, so the Elvis operator returns 0.

How can you use the Elvis operator to throw an exception if a value is null?

A val value = nullable ?: throw Exception()

B val value = nullable ?: return Exception()

C val value = nullable ?: println("Error")

D val value = nullable ?: null

You can throw an exception on the right side of ?: to stop execution if the left side is null.

What is the main benefit of using the Elvis operator in Kotlin?

A Simplifies null checks and provides default values

B Replaces all if statements

C Automatically converts types

D Improves performance by skipping null checks

The Elvis operator simplifies code by handling nulls with default values, making code cleaner and safer.

Explain how the Elvis operator can be chained to handle multiple nullable variables.

Think about checking several variables one after another.

Describe how you can use the Elvis operator to throw an exception when a nullable value is null.

Consider what happens if the left side is null and you want to stop the program.