Custom getters and setters in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a custom getter that returns the name in uppercase.

Kotlin

class Person(val name: String) {
    val upperName: String
        get() = [1]
}

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

Aname.lowercase()

Bname.uppercase()

Cname.length

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase() instead of uppercase()

Returning the original name without conversion

The custom getter returns the name in uppercase using uppercase().

2fill in blank

medium

Complete the code to define a custom setter that sets the age only if it is positive.

Kotlin

class Person {
    var age: Int = 0
        set(value) {
            if ([1]) field = value
        }
}

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

Avalue > 0

Bvalue < 0

Cvalue == 0

Dvalue >= 0

Attempts:

3 left

💡 Hint

Common Mistakes

Using value < 0 which allows negative ages

Using value >= 0 which allows zero age

The setter checks if the new value is greater than zero before setting it.

3fill in blank

hard

Fix the error in the custom setter to avoid infinite recursion.

Kotlin

class Rectangle {
    var width: Int = 0
        set(value) {
            [1] = value
        }
}

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

Afield

Bwidth

Cthis.width

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning to the property name instead of field

Using this.width which also calls the setter

Use field inside the setter to assign the backing field and avoid recursion.

4fill in blank

hard

Fill both blanks to create a custom getter that returns the area of the rectangle.

Kotlin

class Rectangle(val height: Int, val width: Int) {
    val area: Int
        get() = [1] * [2]
}

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

Aheight

Bwidth

Carea

Dthis

Attempts:

3 left

💡 Hint

Common Mistakes

Using area inside its own getter causing recursion

Using this which is not a number

The getter multiplies height and width to calculate the area.

5fill in blank

hard

Fill all three blanks to create a property with a custom getter and setter that keeps the score between 0 and 100.

Kotlin

class Game {
    var score: Int = 0
        get() = [1]
        set(value) {
            field = when {
                value < 0 -> [2]
                value > 100 -> [3]
                else -> value
            }
        }
}

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

Afield

B0

C100

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Getter returning value instead of field

Setter not clamping values correctly

The getter returns the backing field. The setter clamps the score between 0 and 100.

Practice

1. What is the main purpose of custom getters and setters in Kotlin?

easy

A. To create new classes automatically

B. To define functions outside a class

C. To control how properties are read and written

D. To import external libraries

Solution

1. Step 1: Understand property access

   Custom getters and setters allow you to define how a property value is retrieved or changed.

2. Step 2: Identify their purpose

   They help control and protect the data by customizing read/write behavior.

3. Final Answer:

   To control how properties are read and written -> Option C

4. Quick Check:

   Custom getters/setters = control property access [OK]

Hint: Remember: getters/setters control property reading/writing [OK]

Common Mistakes:

• Confusing getters/setters with class creation
• Thinking they define functions outside classes
• Assuming they import libraries

2. Which of the following is the correct syntax to define a custom setter for a Kotlin property age?

easy

A. var age: Int
set(value) { field = value }

B. var age: Int
get(value) { field = value }

C. val age: Int
set(value) { field = value }

D. var age: Int
set { value = field }

Solution

1. Step 1: Check property mutability

   Setter can only be defined for var, not val.

2. Step 2: Verify setter syntax

   The setter uses set(value) { field = value } to assign the new value.

3. Final Answer:

   var age: Int set(value) { field = value } -> Option A

4. Quick Check:

   Setter syntax = set(value) { field = value } [OK]

Hint: Setter needs var and set(value) syntax [OK]

Common Mistakes:

• Using get instead of set for setter
• Defining setter on val property
• Reversing field and value in setter

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

class Person {
    var name: String = ""
        get() = field.uppercase()
        set(value) { field = value.trim() }
}

fun main() {
    val p = Person()
    p.name = "  alice  "
    println(p.name)
}

medium

A. ALICE

B. alice

C. ecila

D. Alice

Solution

1. Step 1: Analyze setter behavior

   Setter trims the input, so " alice " becomes "alice" stored in field.

2. Step 2: Analyze getter behavior

   Getter returns the stored value in uppercase, so "alice" becomes "ALICE".

3. Final Answer:

   ALICE -> Option A

4. Quick Check:

   Setter trims, getter uppercases = ALICE [OK]

Hint: Setter trims, getter uppercases output [OK]

Common Mistakes:

• Ignoring trimming in setter
• Not converting to uppercase in getter
• Assuming original input prints

4. Identify the error in this Kotlin class with custom getter and setter:

class Box {
    var size: Int = 0
        get() = field
        set(value) {
            if (value > 0) field = value
            else field = 0
        }

    fun printSize() {
        println(size)
    }
}

medium

A. Setter does not assign value correctly

B. No error, code works fine

C. Getter should not use field

D. Property size should be val, not var

Solution

1. Step 1: Check setter logic

   Setter assigns field = value if positive, else 0. This is valid.

2. Step 2: Check getter and property type

   Getter returns field, which is correct. Property is var, so setter allowed.

3. Final Answer:

   No error, code works fine -> Option B

4. Quick Check:

   Setter and getter correct = no error [OK]

Hint: Setter with condition is valid; getter uses field correctly [OK]

Common Mistakes:

• Thinking getter can't use field
• Assuming setter must always assign value
• Confusing var and val for setters

5. You want a Kotlin property score that never stores a negative value. Which custom setter implementation ensures this correctly?

hard

A. var score: Int = 0
set(value) { field = value * -1 }

B. var score: Int = 0
set(value) { if (value < 0) field = 0 }

C. var score: Int = 0
set(value) { field = value }

D. var score: Int = 0
set(value) { field = if (value < 0) 0 else value }

Solution

1. Step 1: Understand requirement

   Property must never store negative values; negative inputs become zero.

2. Step 2: Evaluate each setter

   var score: Int = 0 set(value) { field = if (value < 0) 0 else value } sets field to 0 if value is negative, else stores value correctly.

3. Step 3: Check other options

   A stores negative of value, which can be positive or negative incorrectly; B only sets field if negative, ignoring positive values; C stores negatives unchanged.

4. Final Answer:

   var score: Int = 0 set(value) { field = if (value < 0) 0 else value } -> Option D

5. Quick Check:

   Setter with if-else ensures no negatives [OK]

Hint: Use if-else in setter to block negatives [OK]

Common Mistakes:

• Not assigning field for positive values
• Allowing negative values to be stored
• Incorrectly negating values