Causes and Solutions for Kotlin “Expecting an element”

When writing code in Kotlin, you may encounter an error called “Expecting an element”.

This error occurs when the Kotlin compiler is analyzing code and cannot find an element such as an expression, value, or identifier that should normally be present at that location.

Possible causes include forgetting to close parentheses or braces, incorrect placement of commas or operators, mistakes in conditional expressions, and unnecessary symbols in the code.

This article introduces the main causes of the “Expecting an element” error in Kotlin and the basic ways to resolve it.

What Is “Expecting an element”?

“Expecting an element” is a syntax error indicating that a required code element is missing when the compiler analyzes the syntax of the code.

For example, it may occur when there is no value after an operator.

val total = 10 +

In this code, there is no value to be calculated after +.

Because the compiler expects an expression to follow +, a syntax error such as “Expecting an element” may be displayed.

Write the correct value or expression.

val total = 10 + 5

Cause 1: There Is No Value or Expression After an Operator

One of the most basic causes is writing an operator without providing the required value or expression after it.

val result = value *

After *, an expression such as a number or variable is normally required.

Add the required value.

val result = value * 2

Cause 2: A Closing Parenthesis Is Missing

If a closing parenthesis () is missing, the compiler may be unable to correctly analyze the code that follows, causing “Expecting an element” to be displayed.

println("Hello"

In this code, the closing parenthesis for println() is missing.

Add the closing parenthesis.

println("Hello")

The cause may also be an unclosed parenthesis on the line immediately before the line where the error is displayed.

Cause 3: A Closing Brace Is Missing

If braces {} used in functions, classes, if, when, loops, and other structures are missing, syntax analysis may break down and cause an error.

fun main() {
    if (true) {
        println("Hello")
}

In this example, a brace required to close either the if block or the main() block is missing.

Close the corresponding braces correctly.

fun main() {
    if (true) {
        println("Hello")
    }
}

Cause 4: There Is an Unnecessary Comma

If a comma used to separate arguments or elements is placed incorrectly, the compiler may expect another element and display “Expecting an element”.

val numbers = listOf(1, 2, , 3)

In this code, there is no element between the two commas.

Remove the unnecessary comma.

val numbers = listOf(1, 2, 3)

Cause 5: An Argument Is Missing from a Function Call

An error may occur if only a comma remains in a function call or if an expression required as an argument is missing.

showMessage("Hello", )

In this case, the code is written as though another argument follows the comma, but there is actually no element there.

Remove the unnecessary comma or add the required argument.

showMessage("Hello")

Cause 6: A Condition or Expression in an if Statement Is Incomplete

“Expecting an element” may also be displayed when the syntax of an if statement or if expression is incomplete.

if (age >= ) {
    println("Adult")
}

In this example, there is no value to compare against on the right side of >=.

Write the required value.

if (age >= 18) {
    println("Adult")
}

Cause 7: A when Expression Is Incomplete

If there is no processing after a condition or on the right side of -> in a when expression, an error may occur because a required element is missing.

when (value) {
    1 ->
    2 -> println("Two")
}

In this example, there is no operation to execute after 1 ->.

Add the required expression or processing.

when (value) {
    1 -> println("One")
    2 -> println("Two")
}

Cause 8: A Lambda Expression Is Incomplete

A syntax error may also occur if required parameters or processing are missing before or after -> in a lambda expression.

val action = { value -> }

An empty body itself is not always a problem, but while writing a more complex lambda expression, “Expecting an element” may be displayed if the position of -> is incorrect or a required expression is deleted.

Check whether the parameters and processing section of the lambda expression have the correct structure.

val action = { value: Int ->
    println(value)
}

Cause 9: An Unnecessary Symbol Is Included

When code is copied or mistyped during editing, a symbol that has no meaning in Kotlin syntax may be included and cause an error.

val name = "Taro" @

If an unnecessary symbol like this exists at the end of the code or elsewhere, the compiler cannot analyze it correctly.

Remove the unnecessary symbol.

val name = "Taro"

Cause 10: Syntax from Another Language Is Mixed In

If syntax from another programming language such as Java or JavaScript is written directly in Kotlin code, it may not be parsed as Kotlin and can result in an error.

int value = 10;

This is a form used in Java and is not normally written this way in Kotlin.

In Kotlin, write it as follows.

val value: Int = 10

If an error occurs immediately after porting code from another language, check whether it has been correctly rewritten using Kotlin syntax.

Cause 11: There Is a Syntax Error on the Previous Line

The problem is not necessarily on the line where “Expecting an element” is displayed.

If you forget to close a parenthesis or quotation mark on the previous line, the error may be displayed on the following line as a result.

val message = "Hello
val number = 10

In this case, the problem is not the number line, but the missing closing quotation mark in the preceding string.

Close the quotation mark correctly.

val message = "Hello"
val number = 10

Check Matching Parentheses and Braces

When the error is displayed, first check whether parentheses such as (), {}, and [] are correctly matched.

Especially when the code becomes long, it may become difficult to see which parenthesis or brace is closed at which position.

In IDEs such as Android Studio, selecting a parenthesis or brace highlights its matching counterpart, making it easier to check for missing closing characters.

Temporarily Simplify the Code to Identify the Cause

If “Expecting an element” is displayed within a complex expression or long function, temporarily simplifying the part that may contain the problem can make it easier to identify the cause.

For example, if multiple conditions or function calls are written on a single line, separate them into individual variables and check them.

val isAdult = age >= 18

if (isAdult) {
    println("Adult")
}

By dividing the code into smaller units, it becomes easier to identify which expression has broken syntax.

Points to Check When “Expecting an element” Appears

When “Expecting an element” appears, check whether there are any syntactically missing elements or unnecessary symbols around the error location.

• Is there a value or expression after the operator?
• Are parentheses () closed correctly?
• Are braces {} closed correctly?
• Are there any unnecessary commas left in the code?
• Is an argument missing in the middle of a function call?
• Are the conditions or processing of if or when incomplete?
• Is -> positioned correctly in the lambda expression?
• Are any unnecessary symbols included in the code?
• Is syntax from another language such as Java written directly in the code?
• Did you forget to close a quotation mark or parenthesis on the previous line?

Especially with syntax errors, the compiler may detect the error at a position later than the actual cause.

Therefore, it is important to check the code starting from a few lines before the error rather than looking only at the error line.

Summary

Kotlin’s “Expecting an element” is a syntax error displayed when the compiler is analyzing code and cannot find an element such as an expression or value that should be present at that location.

Typical causes include a missing value after an operator, missing closing parentheses or braces, unnecessary commas, mistakes in if or when syntax, and unnecessary symbols in the code.

Basically, the error can be resolved by checking the syntax around the location where the error is displayed, adding missing values or parentheses, or removing unnecessary symbols.

Also, because the actual cause often exists before the line where the error is displayed, it is important to check whether parentheses, quotation marks, operators, and other elements are written correctly in the preceding several lines.

When “Expecting an element” appears, checking the code before and after the error location while considering “what element the compiler expects at this position” makes it easier to identify the cause.