Custom exception classes in Kotlin - Time & Space Complexity

Time Complexity: Custom exception classes

O(n)

Understanding Time Complexity

When we create custom exception classes in Kotlin, we want to know how much time it takes to create and throw these exceptions.

We ask: How does the time to handle exceptions grow as we use them more?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

class MyCustomException(message: String) : Exception(message)

fun checkValue(value: Int) {
    if (value < 0) {
        throw MyCustomException("Negative value not allowed")
    }
}

fun processValues(values: List) {
    for (v in values) {
        checkValue(v)
    }
}
    

This code defines a custom exception and throws it when a value is negative while processing a list of integers.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Looping through the list of values and checking each one.
• How many times: Once for each item in the list (n times).

How Execution Grows With Input

As the list size grows, the number of checks grows the same way.

Input Size (n)	Approx. Operations
10	10 checks
100	100 checks
1000	1000 checks

Pattern observation: The work grows directly with the number of items.

Final Time Complexity

Time Complexity: O(n)

This means the time to process values grows linearly with the number of values.

Common Mistake

[X] Wrong: "Throwing a custom exception takes constant time no matter how many times it happens."

[OK] Correct: Each exception throw involves creating an object and stack trace work, so doing it many times adds up.

Interview Connect

Understanding how exception handling scales helps you write code that stays efficient even when errors happen often.

Self-Check

"What if we changed the list to a sequence that processes items lazily? How would the time complexity change?"

Practice

1. What is the main purpose of creating a custom exception class in Kotlin?

easy

A. To speed up program execution

B. To define a specific type of error with a clear name

C. To automatically fix errors in code

D. To replace all built-in exceptions

Solution

1. Step 1: Understand what exceptions represent

   Exceptions represent errors or unexpected events in a program.

2. Step 2: Purpose of custom exceptions

   Custom exceptions let you name specific error types clearly, making code easier to read and debug.

3. Final Answer:

   To define a specific type of error with a clear name -> Option B

4. Quick Check:

   Custom exceptions = clear error types [OK]

Hint: Custom exceptions give clear names to specific errors [OK]

Common Mistakes:

• Thinking custom exceptions fix errors automatically
• Believing they speed up code execution
• Confusing them with replacing built-in exceptions

2. Which of the following is the correct way to declare a custom exception class named MyError in Kotlin?

easy

A. exception MyError extends Exception

B. fun MyError() : Exception

C. class MyError inherits Exception

D. class MyError : Exception()

Solution

1. Step 1: Recall Kotlin class declaration syntax

   In Kotlin, classes are declared with class ClassName.

2. Step 2: Inherit from Exception class

   Use colon : to inherit, so class MyError : Exception() is correct.

3. Final Answer:

   class MyError : Exception() -> Option D

4. Quick Check:

   Custom exception syntax = class Name : Exception() [OK]

Hint: Use colon : to inherit Exception in class declaration [OK]

Common Mistakes:

• Using 'fun' instead of 'class' to declare exception
• Using 'extends' or 'inherits' which are not Kotlin keywords
• Missing parentheses after Exception

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

class MyException : Exception("Custom error")

fun test() {
  throw MyException()
}

fun main() {
  try {
    test()
  } catch (e: MyException) {
    println(e.message)
  }
}

medium

A. Custom error

B. MyException

C. null

D. No output, program crashes

Solution

1. Step 1: Understand the custom exception message

   The class passes "Custom error" to Exception constructor, so e.message is "Custom error".

2. Step 2: Catch block prints the exception message

   The catch block catches MyException and prints e.message, which is "Custom error".

3. Final Answer:

   Custom error -> Option A

4. Quick Check:

   Exception message printed = Custom error [OK]

Hint: Exception message prints from e.message in catch block [OK]

Common Mistakes:

• Expecting class name instead of message
• Thinking program crashes without output
• Assuming message is null if not set explicitly

4. Identify the error in this Kotlin custom exception class:

class MyException extends Exception() {}

medium

A. Class body cannot be empty

B. Missing parentheses after class name

C. Using 'extends' instead of ':' for inheritance

D. Exception class cannot be inherited

Solution

1. Step 1: Check Kotlin inheritance syntax

   Kotlin uses colon ':' for inheritance, not 'extends'.

2. Step 2: Identify the incorrect keyword

   The code uses 'extends' which is from Java, causing syntax error.

3. Final Answer:

   Using 'extends' instead of ':' for inheritance -> Option C

4. Quick Check:

   Kotlin inheritance uses ':' not 'extends' [OK]

Hint: Use ':' not 'extends' for inheritance in Kotlin [OK]

Common Mistakes:

• Confusing Java syntax with Kotlin
• Thinking empty class body is invalid
• Believing Exception cannot be subclassed

5. You want to create a custom exception InvalidAgeException that takes an age value as a property and shows a message like "Invalid age: 15". Which Kotlin code correctly implements this?

hard

A. class InvalidAgeException(val age: Int) : Exception("Invalid age: $age")

B. class InvalidAgeException(age: Int) : Exception("Invalid age: ${age}")

C. class InvalidAgeException(age: Int) : Exception("Invalid age: $age")

D. class InvalidAgeException(age: Int) : Exception("Invalid age: " + age)

Solution

1. Step 1: Understand primary constructor properties and string interpolation

   In Kotlin, val param: Type creates a read-only property accessible as e.age.

2. Step 2: Constructor param available in super call

   Params (with or without val) are in scope for superclass constructor, use $age for interpolation (braces optional for simple identifiers).

3. Step 3: Evaluate options

   A correctly uses val age: Int for property + $age interpolation. B/C/D lack val, so no age property (only private param). D uses concatenation (valid but less idiomatic).

4. Final Answer:

   class InvalidAgeException(val age: Int) : Exception("Invalid age: $age") -> Option A

5. Quick Check:

   val age: Int + $age interpolation for property + message [OK]

Hint: Use val age: Int and $age for property + message interpolation [OK]

Common Mistakes:

• Omitting 'val' (no public age property)
• Using unnecessary braces ${age} (optional for simple vars)
• Using string concatenation instead of interpolation