String comparison (equals, compareTo) in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin code comparing strings with equals()?

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

Kotlin

fun main() {
    val a = "Hello"
    val b = "hello"
    println(a.equals(b))
    println(a.equals(b, ignoreCase = true))
}

A true\ntrue

B false\ntrue

C false\nfalse

D true\nfalse

💡 Hint

Remember that equals() is case-sensitive by default unless ignoreCase is true.

The first equals() call compares "Hello" and "hello" exactly, so it returns false. The second call ignores case, so it returns true.

❓ Predict Output

intermediate

What does compareTo() return when comparing "apple" and "banana"?

What is the output of this Kotlin code?

Kotlin

fun main() {
    val result = "apple".compareTo("banana")
    println(result)
}

A A negative number less than -1

B 0

C 1

D -1

💡 Hint

compareTo returns a negative number if the first string is lexicographically less than the second.

"apple" is lexicographically less than "banana" because the first characters 'a' (97) and 'b' (98) differ, so compareTo returns a negative number less than -1.

🔧 Debug

advanced

What error does this Kotlin code produce?

Examine this Kotlin code and identify the error it causes.

Kotlin

fun main() {
    val s1: String = null
    val s2 = "test"
    println(s1.equals(s2))
}

A Prints false without error

B RuntimeException: NullPointerException

C Compilation error: Unresolved reference: equals

D Compilation error: Null can not be a value of a non-null type String

💡 Hint

In Kotlin, variables must be declared nullable to hold null.

The variable s1 is declared as non-nullable String and assigned null, which is not allowed. This causes a compilation error.

❓ Predict Output

advanced

What is the output of this Kotlin code using compareTo with ignoreCase?

What will this Kotlin program print?

Kotlin

fun main() {
    val s1 = "Kotlin"
    val s2 = "kotlin"
    println(s1.compareTo(s2, ignoreCase = true))
    println(s1.compareTo(s2))
}

A -32\n0

B 0\n32

C 0\n-32

D 32\n0

💡 Hint

compareTo returns 0 if strings are equal ignoring case, otherwise a positive or negative number.

With ignoreCase=true, "Kotlin" and "kotlin" are equal, so 0 is printed. Without ignoreCase, the difference of 'K' and 'k' ASCII codes is -32.

🧠 Conceptual

expert

How many items are in the resulting map after this Kotlin code?

What is the size of the map produced by this Kotlin code?

Kotlin

fun main() {
    val keys = listOf("a", "A", "b", "B")
    val map = keys.associateWith { it.lowercase() }
    val filteredMap = map.filterKeys { it.equals(it.lowercase(), ignoreCase = true) }
    println(filteredMap.size)
}

A 4

B 2

C 3

D 1

💡 Hint

Check which keys equal their lowercase version ignoring case.

Keys "a", "A", "b", and "B" all equal their lowercase ignoring case, so all 4 keys pass the filter. Therefore, filteredMap.size is 4.