Any type as universal base in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of casting Any to specific types

What is the output of this Kotlin code snippet?

Kotlin

fun main() {
    val value: Any = 42
    when (value) {
        is String -> println("String: $value")
        is Int -> println("Int: $value")
        else -> println("Unknown type")
    }
}

A String: 42

B Int: 42

C Unknown type

D Compilation error

💡 Hint

Remember that 'value' is assigned an Int but typed as Any.

The variable 'value' is of type Any but holds an Int value 42. The 'when' expression checks the actual type at runtime. Since 'value' is an Int, it matches the 'is Int' branch and prints 'Int: 42'.

🧠 Conceptual

intermediate

Why is Any the universal base type in Kotlin?

Which statement best explains why Kotlin uses 'Any' as the universal base type?

A Because all Kotlin classes inherit from 'Any', allowing any value to be stored in variables of type 'Any'.

B Because 'Any' is used only for nullable types.

C Because 'Any' is an interface that all classes implement explicitly.

D Because 'Any' can hold only primitive types like Int and Double.

💡 Hint

Think about inheritance and type hierarchy in Kotlin.

'Any' is the root of the Kotlin class hierarchy. All classes inherit from 'Any' implicitly, so variables of type 'Any' can hold any non-null object.

🔧 Debug

advanced

Identify the runtime error with Any casting

What runtime error will this Kotlin code produce?

Kotlin

fun main() {
    val obj: Any = "Hello"
    val num: Int = obj as Int
    println(num)
}

A Prints 'Hello' without error

B Compilation error due to invalid cast

C ClassCastException at runtime

D Prints 0 due to default conversion

💡 Hint

Casting a String to Int directly is unsafe.

The code tries to cast a String object to Int using 'as'. This compiles but fails at runtime with ClassCastException because the actual object is not an Int.

📝 Syntax

advanced

Which code snippet correctly checks type of Any?

Which of the following Kotlin snippets correctly checks if a variable of type Any holds a String and prints it?

A if (obj is String()) println(obj) else println("Not a String")

B if (obj instanceof String) println(obj) else println("Not a String")

C if (obj.type == String) println(obj) else println("Not a String")

D if (obj is String) println(obj) else println("Not a String")

💡 Hint

Remember Kotlin uses 'is' for type checking.

Kotlin uses 'is' keyword to check type at runtime. Option D uses correct syntax. Option D uses Java syntax 'instanceof' which is invalid in Kotlin. Option D and D are invalid syntax.

🚀 Application

expert

Result of storing different types in a List

What will be the output of this Kotlin program?

Kotlin

fun main() {
    val items: List<Any> = listOf(10, "Kotlin", 3.14, true)
    for (item in items) {
        when (item) {
            is Int -> print("I")
            is String -> print("S")
            is Double -> print("D")
            is Boolean -> print("B")
            else -> print("?")
        }
    }
}

A ISDB

B IDSB

C ISD?

D Compilation error

💡 Hint

Check the type of each element in the list and the corresponding print letter.

The list contains Int(10), String("Kotlin"), Double(3.14), and Boolean(true). The when expression prints 'I' for Int, 'S' for String, 'D' for Double, and 'B' for Boolean. So the output is 'ISDB'.