Kotlin Kotlin Type System and Null Safety 3

Question 1

What is the key difference between `Any` and `Any?` in Kotlin?

Accepted Answer

Any? is the supertype of all types including nullable, while Any excludes null

Answer

`Any?` is the supertype of all Kotlin types including nullable types, while `Any` is the supertype only of non-nullable types and cannot hold null.

Question 2

What is a 'platform type' in Kotlin?

Accepted Answer

A type from Java interop with unknown nullability, denoted as Type!

Answer

Platform types arise when Kotlin code uses Java APIs without nullability annotations; they're shown as `Type!` and can be treated as either nullable or non-nullable.

Question 3

How does Kotlin differ from Java in handling numeric type conversions?

Accepted Answer

Kotlin requires explicit conversion functions like toInt() or toLong()

Answer

Unlike Java, Kotlin does not perform implicit numeric type conversions; you must explicitly call conversion functions like `toInt()`, `toLong()`, or `toDouble()`.

Question 4

What is `Unit` in Kotlin equivalent to in Java?

Accepted Answer

void

Answer

`Unit` is Kotlin's equivalent of Java's `void` — it's the return type of functions that don't produce a meaningful value, but unlike void it is an actual singleton type.

Question 5

What is the primary benefit of sealed classes in Kotlin's type system?

Accepted Answer

They allow exhaustive when expressions without an else branch

Answer

Since all subclasses of a sealed class are known at compile time, `when` expressions can be exhaustive — covering every subclass means no `else` branch is needed.

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Kotlin Kotlin Type System and Null Safety 3