Operator overloading concept in Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kotlin operator overloading code?

Consider this Kotlin class that overloads the plus operator. What will be printed when the code runs?

Kotlin

data class Point(val x: Int, val y: Int) {
    operator fun plus(other: Point) = Point(x + other.x, y + other.y)
}

fun main() {
    val p1 = Point(2, 3)
    val p2 = Point(4, 5)
    val p3 = p1 + p2
    println(p3)
}

A Point(x=6, y=8)

B Point(x=8, y=10)

C Point(x=2, y=3) + Point(x=4, y=5)

D Compilation error: operator plus not defined

💡 Hint

Remember that plus adds the x and y values separately.

The plus operator adds the x and y values of two Point objects. So (2+4, 3+5) = (6, 8).

❓ Predict Output

intermediate

What does this Kotlin code print when overloading the unary minus operator?

Look at this Kotlin class that overloads the unary minus operator. What is the output?

Kotlin

data class Vector(val x: Int, val y: Int) {
    operator fun unaryMinus() = Vector(-x, -y)
}

fun main() {
    val v = Vector(7, -3)
    println(-v)
}

A Vector(x=-7, y=3)

B Vector(x=7, y=-3)

C Vector(x=-7, y=-3)

D Runtime error: operator unaryMinus not found

💡 Hint

The unary minus operator negates each coordinate.

The unary minus operator returns a new Vector with both x and y negated. So (7, -3) becomes (-7, 3).

❓ Predict Output

advanced

What is the output of this Kotlin code with operator overloading and custom class?

This Kotlin class overloads the times operator. What will be printed?

Kotlin

class Matrix(val value: Int) {
    operator fun times(other: Matrix) = Matrix(this.value * other.value)
    override fun toString() = "Matrix(value=$value)"
}

fun main() {
    val m1 = Matrix(3)
    val m2 = Matrix(4)
    val m3 = m1 * m2
    println(m3)
}

A Matrix(value=7)

B Matrix(value=12)

C Matrix(value=34)

D Compilation error: operator times not defined

💡 Hint

The times operator multiplies the values inside the matrices.

The times operator returns a new Matrix with the product of the two values: 3 * 4 = 12.

❓ Predict Output

advanced

What error does this Kotlin code raise when overloading the increment operator?

Examine this Kotlin class that tries to overload the increment operator ++. What error occurs when compiling?

Kotlin

class Counter(var count: Int) {
    operator fun inc() {
        count += 1
    }
}

fun main() {
    val c = Counter(5)
    c++
    println(c.count)
}

A Runtime error: inc operator not supported

B 6

C 5

D Compilation error: inc operator must return a value

💡 Hint

The inc operator must return the updated object.

The inc operator function must return the incremented object. Here it returns Unit (nothing), causing a compilation error.

🧠 Conceptual

expert

Which Kotlin operator overloading function signature is correct for the 'contains' operator?

In Kotlin, to overload the in operator (used like item in collection), which function signature is correct?

A operator fun in(item: T): Boolean

B operator fun has(item: T): Boolean

C operator fun contains(item: T): Boolean

D operator fun contains(): Boolean

💡 Hint

The function name must be contains and take one parameter.

The in operator calls the contains function with the item as parameter, returning a Boolean.