Elvis operator (?:) for default values in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Elvis operator (?:) do in Kotlin?

The Elvis operator returns the value on its left if it is not null; otherwise, it returns the value on its right. It helps provide default values when dealing with nullable variables.

beginner

How do you use the Elvis operator to assign a default value to a nullable variable?

You write: val result = nullableValue ?: defaultValue. If nullableValue is null, result gets defaultValue.

beginner

Example: What is the output of val name: String? = null; println(name ?: "Guest")?

The output is Guest because name is null, so the Elvis operator returns the default string "Guest".

intermediate

Can the Elvis operator be chained in Kotlin?

Yes, you can chain Elvis operators like val result = a ?: b ?: c. It returns the first non-null value from left to right.

beginner

Why is the Elvis operator useful in real-life Kotlin programming?

It simplifies code by avoiding explicit null checks and providing easy default values, making programs safer and cleaner.

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

A The right side value

B An error

C Null

D The left side value

The Elvis operator returns the left side value if it is not null.

Which Kotlin code uses the Elvis operator correctly to provide a default value?

A val x = nullable ?: default

B val x = nullable ? default

C val x = nullable || default

D val x = nullable && default

The Elvis operator syntax is ?:, so nullable ?: default is correct.

What will val age: Int? = null; val result = age ?: 18 assign to result?

A 0

B null

C 18

D Error

Since age is null, the Elvis operator returns the default value 18.

Can the Elvis operator be used with non-nullable types?

A No, only with nullable types

B Yes, always

C Only with strings

D Only with numbers

Yes, the Elvis operator can be used with non-nullable types on the left side (though redundant since the right side is never used), in addition to nullable types.

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

A To shorten code by avoiding explicit null checks

B To create loops

C To declare variables

D To handle exceptions

The Elvis operator helps shorten code by providing default values without explicit null checks.

Explain how the Elvis operator (?:) works in Kotlin and give a simple example.

Think about how to provide a fallback value when something might be null.

Describe a real-life situation where using the Elvis operator can make your Kotlin code cleaner and safer.

Imagine you ask for a user's name but they might not enter it.