Operator overloading concept in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to overload the plus operator for the Point class.

Kotlin

operator fun Point.plus(other: Point): Point = Point(this.x [1] other.x, this.y + other.y)

Drag options to blanks, or click blank then click option'

A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using a minus or other operator instead of plus.

Forgetting the operator keyword.

The plus operator is overloaded by defining operator fun plus and using the + symbol to add the x coordinates.

2fill in blank

medium

Complete the code to overload the times operator for the Vector class.

Kotlin

operator fun Vector.times(scalar: Int): Vector = Vector(this.x [1] scalar, this.y * scalar)

Drag options to blanks, or click blank then click option'

A+

B/

C*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using plus or minus instead of multiplication.

Forgetting to mark the function with operator.

The times operator multiplies each coordinate by the scalar using the * symbol.

3fill in blank

hard

Fix the error in the operator overloading function to correctly overload the unary minus operator.

Kotlin

operator fun Point.[1](): Point = Point(-this.x, -this.y)

Drag options to blanks, or click blank then click option'

Anot

Bminus

CunaryPlus

DunaryMinus

Attempts:

3 left

💡 Hint

Common Mistakes

Using minus which requires a parameter.

Using unaryPlus instead of unaryMinus.

The unary minus operator is overloaded by defining operator fun unaryMinus().

4fill in blank

hard

Fill both blanks to overload the compareTo operator for the Box class to compare volumes.

Kotlin

operator fun Box.compareTo(other: Box): Int = this.volume() [1] other.volume() [2] 0

Drag options to blanks, or click blank then click option'

A-

B+

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using comparison operators like > or < instead of subtraction.

Omitting the operator keyword.

The compareTo operator returns the difference of volumes, so subtract volumes and add zero to complete the expression.

5fill in blank

hard

Fill all three blanks to overload the get operator for the Matrix class to access elements by row and column.

Kotlin

operator fun Matrix.get([1]: Int, [2]: Int): Int = data[[1]][[3]]

Drag options to blanks, or click blank then click option'

Arow

Bcol

Ccolumn

Dindex

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent parameter names.

Using the same name for both parameters.

The get operator uses two parameters, typically named row and column. The data is accessed by data[row][column].

Practice

1. What does operator overloading in Kotlin allow you to do?

easy

A. Disable operators for certain classes

B. Change the meaning of built-in types like Int or String

C. Create new operators not available in Kotlin

D. Use standard operators like + or * with your own classes

Solution

1. Step 1: Understand operator overloading purpose

   Operator overloading lets you define how operators like + work with your own classes.

2. Step 2: Check options meaning

   Only Use standard operators like + or * with your own classes correctly states this ability. Options A, B, and C are incorrect because Kotlin does not let you change built-in types, create new operators, or disable operators this way.

3. Final Answer:

   Use standard operators like + or * with your own classes -> Option D

4. Quick Check:

   Operator overloading = Use operators with custom classes [OK]

Hint: Operator overloading means using +, * with your own classes [OK]

Common Mistakes:

• Thinking you can create new operators
• Believing it changes built-in types
• Confusing disabling operators with overloading

2. Which of the following is the correct syntax to overload the plus operator in a Kotlin class?

easy

A. operator fun plus(other: MyClass): MyClass { ... }

B. fun plus(other: MyClass): MyClass { ... }

C. override fun plus(other: MyClass): MyClass { ... }

D. fun operator plus(other: MyClass): MyClass { ... }

Solution

1. Step 1: Recall operator function syntax

   In Kotlin, to overload an operator, the function must be marked with the keyword operator before the function declaration.

2. Step 2: Analyze options

   operator fun plus(other: MyClass): MyClass { ... } correctly uses operator fun plus(...). fun plus(other: MyClass): MyClass { ... } misses the operator keyword, C wrongly uses override, and D has incorrect keyword order.

3. Final Answer:

   operator fun plus(other: MyClass): MyClass { ... } -> Option A

4. Quick Check:

   Operator keyword before function = Correct syntax [OK]

Hint: Always put 'operator' before function to overload operators [OK]

Common Mistakes:

• Omitting the 'operator' keyword
• Using 'override' instead of 'operator'
• Placing 'operator' after 'fun'

3. What will be the output of this Kotlin code?

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(1, 2)
    val p2 = Point(3, 4)
    val p3 = p1 + p2
    println(p3)
}

medium

A. Point(x=4, y=6)

B. p1 + p2

C. Compilation error

D. Point(4, 6)

Solution

1. Step 1: Understand operator plus function

   The plus operator adds the x and y values of two Point objects and returns a new Point with summed coordinates.

2. Step 2: Calculate the result of p1 + p2

   p1 has (1, 2), p2 has (3, 4). Adding gives (4, 6). Printing p3 calls data class's toString(), which outputs 'Point(x=4, y=6)'.

3. Final Answer:

   Point(x=4, y=6) -> Option A

4. Quick Check:

   p1 + p2 = Point(x=4, y=6) [OK]

Hint: Data class toString shows property names; sum coordinates [OK]

Common Mistakes:

• Expecting just coordinates without property names
• Thinking '+' prints expression instead of result
• Assuming compilation error without operator keyword

4. Identify the error in this Kotlin code that tries to overload the minus operator:

class Counter(var count: Int) {
    fun minus(other: Counter): Counter {
        return Counter(count - other.count)
    }
}

medium

A. Wrong return type; should be Int instead of Counter

B. Missing 'operator' keyword before the minus function

C. Function name should be 'operatorMinus' instead of 'minus'

D. Cannot overload minus operator for classes

Solution

1. Step 1: Check operator overloading syntax

   To overload an operator in Kotlin, the function must have the 'operator' keyword before its declaration.

2. Step 2: Analyze the code

   The minus function lacks the 'operator' keyword, so Kotlin won't treat it as operator overloading, causing errors when using '-'.

3. Final Answer:

   Missing 'operator' keyword before the minus function -> Option B

4. Quick Check:

   Operator functions need 'operator' keyword [OK]

Hint: Operator functions must start with 'operator' keyword [OK]

Common Mistakes:

• Forgetting the 'operator' keyword
• Changing function name incorrectly
• Assuming operator overloading is not allowed

5. Given this Kotlin class:

class Vector(val x: Int, val y: Int) {
    operator fun plus(other: Vector) = Vector(x + other.x, y + other.y)
    operator fun times(scalar: Int) = Vector(x * scalar, y * scalar)
}

What is the result of this expression?

val v1 = Vector(2, 3)
val v2 = Vector(1, 1)
val result = (v1 + v2) * 2
println("(${result.x}, ${result.y})")

hard

A. (3, 4)

B. (4, 6)

C. (6, 8)

D. Compilation error due to operator precedence

Solution

1. Step 1: Evaluate v1 + v2

   v1 is (2,3), v2 is (1,1). Adding gives Vector(3,4).

2. Step 2: Multiply the result by 2

   Vector(3,4) times 2 gives Vector(6,8).

3. Step 3: Print the result

   Printing prints (6, 8) as expected.

4. Final Answer:

   (6, 8) -> Option C

5. Quick Check:

   (v1 + v2) * 2 = (6, 8) [OK]

Hint: Evaluate plus first, then times; operator overloading respects precedence [OK]

Common Mistakes:

• Multiplying v2 by 2 instead of the sum
• Ignoring operator precedence
• Expecting compilation error