Comparison operators in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained comparison operators

What is the output of this Kotlin code snippet?

Kotlin

fun main() {
    val a = 5
    val b = 10
    val c = 15
    println(a < b && b < c)
}

A false

B true

C Compilation error

D Runtime exception

💡 Hint

Think about how logical AND works with comparison operators.

The expression 'a < b && b < c' checks if a is less than b AND b is less than c. Both are true, so the result is true.

❓ Predict Output

intermediate

Result of equality and identity operators

What will be printed by this Kotlin code?

Kotlin

fun main() {
    val x = "hello"
    val y = "hello"
    println(x == y)
    println(x === y)
}

A true\nfalse

B false\nfalse

C false\ntrue

D true\ntrue

💡 Hint

Remember the difference between '==' and '===' in Kotlin.

'==' checks structural equality (content), so x == y is true. '===' checks referential equality (same object). Since both are identical string literals, they refer to the same instance in the constant pool, so true.

❓ Predict Output

advanced

Output of comparison with nullable types

What is the output of this Kotlin code?

Kotlin

fun main() {
    val a: Int? = null
    val b: Int? = 5
    println(a < b)
}

A Compilation error

B true

C false

D Runtime exception

💡 Hint

Kotlin's type system prevents direct comparisons involving nullable types.

Kotlin does not define comparison operators like '<' for nullable types (Int?) because they do not implement Comparable. This results in a compilation error.

❓ Predict Output

advanced

Output of custom compareTo implementation

Given this Kotlin class and code, what is printed?

Kotlin

class Box(val size: Int) : Comparable<Box> {
    override fun compareTo(other: Box): Int = this.size - other.size
}

fun main() {
    val box1 = Box(3)
    val box2 = Box(5)
    println(box1 < box2)
}

A Compilation error

B false

C true

D Runtime exception

💡 Hint

Check how the compareTo function affects the '<' operator.

The '<' operator uses compareTo. Since 3 - 5 is negative, box1 < box2 is true.

🧠 Conceptual

expert

Behavior of comparison operators with floating-point NaN

In Kotlin, what is the result of comparing a Double.NaN with any number using '<' or '>' operators?

A Both '<' and '>' return false when comparing NaN with any number

B '<' returns true and '>' returns false when comparing NaN with any number

C '<' returns false and '>' returns true when comparing NaN with any number

D Both '<' and '>' throw a runtime exception when comparing NaN with any number

💡 Hint

Recall how IEEE floating-point standard treats NaN in comparisons.

According to IEEE rules, any comparison with NaN using '<' or '>' returns false, no exception is thrown.