Kotlin Kotlin Type System and Null Safety

Question 1

What symbol is appended to a type to make it nullable in Kotlin?

Accepted Answer

?

Answer

In Kotlin, appending `?` to a type name makes it nullable, allowing the variable to hold null values.

Question 2

What does the safe call operator `?.` return when the receiver is null?

Accepted Answer

null

Answer

The safe call operator `?.` returns null instead of throwing an exception when the receiver is null.

Question 3

Which operator in Kotlin throws KotlinNullPointerException if the value is null?

Accepted Answer

!!

Answer

The `!!` non-null assertion operator converts a nullable type to non-nullable and throws KotlinNullPointerException if the value is null.

Question 4

What is the Elvis operator `?:` used for in Kotlin?

Accepted Answer

Providing a default value when an expression is null

Answer

The Elvis operator `?:` returns the left-hand value if it's not null, or the right-hand value as a fallback when it is null.

Question 5

After a null check `if (x != null)`, Kotlin automatically treats `x` as non-nullable inside the block. This is called:

Accepted Answer

Smart casting

Answer

Smart casting is when Kotlin automatically casts a variable to a non-nullable type after the compiler verifies through a null check that it cannot be null.

Kotlin Practice Test

Kotlin Practice Test

Kotlin Kotlin Type System and Null Safety