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try/catch

Learn to catch errors with try/catch.

try/catch: catching errors

A piece of code may throw an error; a try block wraps that code, catch catches the error. The program then continues without crashing.

try {
    val x = 10 / 0
} catch (e: ArithmeticException) {
    println("Error: ${e.message}")
}

If the code inside try fails, control jumps to catch. The caught object is bound to e; e.message carries the error text. Catching the right exception type prevents unexpected failures.

Specific exception types

Each error type points to a different situation. The most common: ArithmeticException, NumberFormatException, NullPointerException, IndexOutOfBoundsException.

try {
    val n = "abc".toInt()
} catch (e: NumberFormatException) {
    println("Not a number")
}

The right type matters for handling the error well. For unknown errors you can catch Exception; but specific types give clearer information. A wrong type lets the error slip past.

Practice Wrap division in try/catch

Inside a try block write val x = 10 / 0. Catch ArithmeticException and print "Error" with println.

Starter code

Main.kt
fun main() {
    // Wrap a division in try; catch the error and print Error
}

Sample solution

Main.kt
fun main() {
    try {
        val x = 10 / 0
    } catch (e: ArithmeticException) {
        println("Error")
    }
}

Expected output

Hata

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What does the catch block do?

  • It throws an error
  • It must ignore the error
  • It repeats the error
  • It catches the error Correct answer

Explanation: catch catches the error raised inside try.

2 Fill in the blank: write catch

Question 
try {
    val x = 10 / 0
} ____ (e: ArithmeticException) {
    println("Error")
}
Answer 
try {
    val x = 10 / 0
} catch (e: ArithmeticException) {
    println("Error")
}

Explanation: catch catches the ArithmeticException.

3 Match exception to scenario

Term Meaning
ArithmeticException Division error
NumberFormatException Conversion error
IndexOutOfBoundsException Array bound
NullPointerException Null access

All lessons in Beginner

1 Kotlin basics

  1. What is Kotlin?
  2. Your first program
  3. The main function
  4. Comments
  5. String templates
  6. Summary - Kotlin basics

2 Variables

  1. val and var
  2. Type inference
  3. const
  4. lateinit
  5. by lazy
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. Boolean and Char
  4. String
  5. Any and Unit
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Elvis operator
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String templates
  3. String methods
  4. substring
  5. split and replace
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. if expression
  4. when
  5. when expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Creating arrays
  2. Array access
  3. Array size
  4. Array loop
  5. Array methods
  6. Summary - Arrays

11 Lists

  1. Creating lists
  2. List operations
  3. List access
  4. List iteration
  5. List methods
  6. Summary - Lists

12 Maps and Sets

  1. Creating sets
  2. Set operations
  3. Creating maps
  4. Map operations
  5. Map iteration
  6. Summary - Maps and Sets

13 Functions

  1. Defining functions
  2. Return values
  3. Expression body
  4. Default parameters
  5. Named arguments
  6. Summary - Functions

14 Null safety

  1. Nullable types
  2. ?, !! and ?:
  3. let
  4. Null check
  5. lateinit
  6. Summary - Null safety

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. Regex
  2. matches and find
  3. replace
  4. StringBuilder
  5. trim and pad
  6. Summary - Advanced strings

17 Enums

  1. enum class
  2. Enum values
  3. Enum properties
  4. when with enum
  5. Enum and range
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. try expression
  5. Custom exceptions
  6. Summary - Exceptions

19 Class basics

  1. class
  2. Constructor
  3. Properties
  4. Methods
  5. this
  6. Summary - Class basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together