Why null safety is Kotlin's defining feature - Challenge Your Understanding

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code with null safety?

Consider the following Kotlin code snippet. What will it print when run?

Kotlin

fun main() {
    val name: String? = null
    println(name?.length ?: "No name")
}

A Throws NullPointerException

B 0

C null

D No name

💡 Hint

Look at the safe call operator and the Elvis operator usage.

The variable 'name' is nullable (String?). The safe call operator '?.' checks if 'name' is null before accessing 'length'. Since 'name' is null, the Elvis operator '?:' returns "No name" instead of throwing an error.

🧠 Conceptual

intermediate

Why does Kotlin distinguish between nullable and non-nullable types?

Why is it important that Kotlin has separate types for nullable and non-nullable variables?

A To allow variables to change type at runtime

B To prevent null pointer exceptions by forcing explicit handling of nulls

C To make all variables nullable by default

D To make the code run faster by avoiding null checks

💡 Hint

Think about common errors in other languages caused by null values.

Kotlin's type system forces developers to explicitly handle nullable types, which helps avoid null pointer exceptions that are common in many other languages.

🔧 Debug

advanced

What error does this Kotlin code produce?

Examine the code below. What error will the Kotlin compiler report?

Kotlin

fun main() {
    val text: String = null
    println(text.length)
}

A Null can not be a value of a non-null type String

B Unresolved reference: length

C NullPointerException at runtime

D No error, prints 0

💡 Hint

Look at the variable declaration and its assigned value.

The variable 'text' is declared as a non-nullable String but assigned null, which is not allowed. The compiler reports a type mismatch error.

📝 Syntax

advanced

Which Kotlin code snippet correctly uses the safe call operator?

Select the code snippet that safely accesses the length of a nullable String variable 'input'.

A val length = input?.length

B val length = input ?: input.length

C val length = input!! .length

D val length = input.length

💡 Hint

Safe call operator is used with '?.' syntax.

Option A uses the safe call operator '?.' which safely accesses 'length' only if 'input' is not null, otherwise returns null.

🚀 Application

expert

What is the output of this Kotlin code demonstrating null safety with let?

Analyze the following Kotlin code and select the output it produces.

Kotlin

fun main() {
    val name: String? = "Kotlin"
    name?.let {
        println("Name length is ${it.length}")
    } ?: println("Name is null")
}

A Name is null

B Name length is null

C Name length is 6

D Throws NullPointerException

💡 Hint

The 'let' function runs only if the variable is not null.

Since 'name' is not null, the 'let' block executes and prints the length of the string 'Kotlin' which is 6.