When as an Expression

What Is a 'when' Expression?

A 'when' expression in Kotlin is a flexible way to handle multiple conditions. It is similar to a switch statement in Java, but more powerful and concise. You use it to choose what your code should do based on different values or conditions.

How 'when' Expressions Work

• You provide a value or condition to the when keyword;
• Each branch checks if the value matches a specific case;
• The first matching branch runs its code block;
• If no branches match, the else branch runs (if provided).

Using 'when' as an Expression

A 'when' expression can return a value. You can assign the result of a when directly to a variable:

val result = when (number) {
    1 -> "One"
    2 -> "Two"
    else -> "Other"
}

Here, result will hold the string that matches the value of number.

Why Use 'when' Expressions?

• Simplifies complex if-else chains;
• Improves code readability and maintainability;
• Supports matching multiple values, ranges, or conditions in each branch.