Custom getters and setters in Kotlin - Time & Space Complexity

Time Complexity: Custom getters and setters

O(1)

Understanding Time Complexity

When using custom getters and setters in Kotlin, it's important to know how often these methods run as your program works.

We want to find out how the time to run changes when we access or change properties with custom code.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

class Rectangle(var width: Int, var height: Int) {
    var area: Int = 0
        get() = width * height
        set(value) {
            field = value
            width = value / height
        }
}

fun main() {
    val rect = Rectangle(10, 5)
    println(rect.area)
    rect.area = 50
    println(rect.width)
}

This code defines a rectangle with custom getter and setter for the area property.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The getter multiplies width and height each time area is accessed.
• How many times: Once per access; no loops or recursion involved.

How Execution Grows With Input

Each time you get or set the area, the operations run once, no matter the size of width or height.

Input Size (n)	Approx. Operations
10	1 multiplication or division
100	1 multiplication or division
1000	1 multiplication or division

Pattern observation: The number of operations stays the same regardless of input size.

Final Time Complexity

Time Complexity: O(1)

This means accessing or setting the property takes the same short time no matter the values involved.

Common Mistake

[X] Wrong: "Custom getters and setters slow down the program a lot as values get bigger."

[OK] Correct: The operations inside getters and setters run once per access, so their time does not grow with the size of the values.

Interview Connect

Understanding how custom getters and setters work helps you explain property access performance clearly and confidently in real projects.

Self-Check

"What if the getter computed the area by looping over a list of rectangles? How would the time complexity change?"

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