Safe casts with as? in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the safe cast operator as? do in Kotlin?

It tries to cast a value to a specified type. If the cast is not possible, it returns null instead of throwing an exception.

beginner

How is as? different from the regular as cast in Kotlin?

as throws a ClassCastException if the cast fails, while as? returns null safely without crashing the program.

beginner

What will be the result of val x: String? = obj as? String if obj is an Int?

The result will be null because obj cannot be safely cast to String.

intermediate

Why is using as? useful in Kotlin programming?

It helps avoid program crashes by safely handling type casts that might fail, making code more robust and easier to maintain.

beginner

Write a simple Kotlin code snippet using as? to safely cast an Any type to String.

val obj: Any = 123 val str: String? = obj as? String println(str) // prints null because obj is not a String

What does val x = obj as? String return if obj is an Int?

A null

B Throws ClassCastException

C The integer value

D Empty string

as? returns null if the cast fails instead of throwing an exception.

Which operator in Kotlin safely casts a value and returns null if it fails?

A as?

B as

C is

D !!

as? is the safe cast operator that returns null on failure.

What happens if you use as to cast an incompatible type?

A Returns null

B Returns default value

C Throws ClassCastException

D Compiles but ignores cast

The regular as operator throws a ClassCastException if the cast is invalid.

Which of these is a benefit of using as??

A Forces non-null values

B Improves performance by skipping checks

C Automatically converts types

D Avoids program crashes on bad casts

as? avoids crashes by returning null instead of throwing exceptions.

If val y = obj as? String and y is null, what does that mean?

A The cast succeeded

B <code>obj</code> was not a String

C <code>obj</code> was a String

D The program crashed

Null means the cast failed because obj was not of type String.

Explain how the safe cast operator as? works in Kotlin and why it is useful.

Think about what happens when a cast might fail.

Write a Kotlin example using as? to safely cast an Any variable to a String and handle the null case.

Try to cast and then check if the result is null before using it.