Sealed classes in Android Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a sealed class named Shape.

Android Kotlin

sealed class [1]

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AShape

Bshape

CShapes

DshapeClass

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or plural forms for the class name.

The sealed class must be named exactly Shape as per the instruction.

2fill in blank

medium

Complete the code to declare a subclass Circle inside the sealed class Shape.

Android Kotlin

sealed class Shape {
    data class [1](val radius: Double) : Shape()
}

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ASquare

BCircle

CTriangle

DRectangle

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different shape name than Circle.

Forgetting to inherit from Shape.

The subclass inside Shape should be named Circle as per the instruction.

3fill in blank

hard

Fix the error in the when expression to handle all Shape subclasses without else.

Android Kotlin

fun area(shape: Shape): Double = when(shape) {
    is Shape.Circle -> 3.14 * shape.radius * shape.radius
    is Shape.Square -> shape.side * shape.side
    [1]
}

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Aelse -> 0.0

Bis Shape.Shape -> 0.0

Cis Shape.Triangle -> 0.5 * shape.base * shape.height

Dis Shape.Rectangle -> shape.length * shape.width

Attempts:

3 left

💡 Hint

Common Mistakes

Using else instead of explicit subclass cases.

Adding a case for the sealed class itself.

To avoid using else, all subclasses must be handled explicitly. Adding is Shape.Triangle covers another subclass.

4fill in blank

hard

Fill both blanks to declare two subclasses Rectangle and Triangle inside sealed class Shape.

Android Kotlin

sealed class Shape {
    data class [1](val length: Double, val width: Double) : Shape()
    data class [2](val base: Double, val height: Double) : Shape()
}

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

ARectangle

BCircle

CTriangle

DSquare

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up class names or using unrelated names.

The subclasses are named Rectangle and Triangle as per the instruction.

5fill in blank

hard

Fill all three blanks to create a when expression that returns area for each Shape subclass.

Android Kotlin

fun area(shape: Shape): Double = when(shape) {
    is Shape.Circle -> 3.14 * shape.radius * shape.radius
    is Shape.Rectangle -> shape.length * shape.width
    is Shape.Triangle -> [1] * shape.base * shape.height
}

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

A3

B1

C2

D0.5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 2 or 3 instead of 0.5.

Forgetting the multiplier.

The area of a triangle is 0.5 times base times height.