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try expression

Learn to use try as an expression in Kotlin.

try as an expression: returns a value

In Kotlin try is an expression; it yields a value. The catch block can also return a value; that lets you give a fallback.

val n = try {
    "42".toInt()
} catch (e: NumberFormatException) {
    0
}
// n = 42

On success the last line of the try block, on error the last line of the catch block is the result. This builds a flow similar to if/else. The result can be assigned directly to a variable.

Nullable results in try expressions

If the catch block returns null, the result may be null. The variable then becomes nullable; safe access is needed.

val n: Int? = try {
    "abc".toInt()
} catch (e: NumberFormatException) {
    null
}
println(n ?: -1)  // -1

The Elvis operator ?: gives a fallback for a null value. This lets you handle nullable results safely. This approach makes it easy to silently fall back when a conversion fails.

Practice Convert a string to a number

With a try expression, call "42".toInt(); catch NumberFormatException and return 0. Assign the result to val n and print it with println.

Starter code

Main.kt
fun main() {
    // Convert a string with a try expression; fall back to 0, print the result
}

Sample solution

Main.kt
fun main() {
    val n = try {
        "42".toInt()
    } catch (e: NumberFormatException) {
        0
    }
    println(n)
}

Expected output

42

Questions and answers

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

1 What does `val n = try { x.toInt() } catch (e) { 0 }` do?

  • It writes 0 to n
  • It writes null to n
  • It writes the try value to n Correct answer
  • It gives a compile error

Explanation: On no error the try value, on error the catch 0 goes to n.

2 Fill in the blank: try expression

Question 
val n = ____ { "42".toInt() } catch (e: NumberFormatException) { 0 }
Answer 
val n = try { "42".toInt() } catch (e: NumberFormatException) { 0 }

Explanation: the try expression yields a value.

3 Match part to role

Term Meaning
try { } Trial
catch { } Fallback value
val n = Assignment
.toInt() Conversion

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