if-else Expressions in Kotlin

Analogy categoryAnalogies

Introduction

In Kotlin, if-else is used for conditional branching just like in most languages, but with a key difference: if is an expression, not just a statement. That means an if-else block can produce a value that you can assign to a variable or return from a function. Because of this, Kotlin has no separate ternary operator (the ? : syntax from Java or C) - a single-line if-else expression fills that role instead.

🏏

Cricket analogy: Like a third umpire's review directly producing the final decision (out/not out) shown on the scoreboard, Kotlin's if-else directly produces a value you can assign, so there's no need for a separate ternary shorthand.

Syntax

kotlin

// As a statement
if (condition) {
    // do something
} else {
    // do something else
}

// As an expression
val result = if (condition) valueIfTrue else valueIfFalse

// Multi-branch
if (condition1) {
    // ...
} else if (condition2) {
    // ...
} else {
    // ...
}

Explanation

When if is used as a statement, the branches perform actions and the return value (if any) is ignored. When used as an expression, the last line of each branch becomes the value of that branch, and both branches must be present and produce a compatible type for the value to be usable. Because Kotlin can infer the type of the whole expression from its branches, val max = if (a > b) a else b reads almost exactly like a ternary expression but stays fully readable with braces when the logic grows more complex.

🏏

Cricket analogy: Like comparing two batsmen's strike rates where val higher = if (rateA > rateB) rateA else rateB picks the winner, both branches must yield a number for the comparison to produce a usable result, unlike a used-and-discarded review.

Example

kotlin

fun main() {
    val a = 10
    val b = 20

    // if-else as an expression
    val max = if (a > b) a else b
    println("Max value is: $max")

    // if-else as a statement with multiple branches
    val score = 72
    val grade = if (score >= 90) {
        "A"
    } else if (score >= 75) {
        "B"
    } else if (score >= 60) {
        "C"
    } else {
        "F"
    }
    println("Grade: $grade")
}

// Output:
// Max value is: 20
// Grade: C

Key Takeaways

if in Kotlin can be used as a statement or as an expression that returns a value.
Because if-else is an expression, Kotlin does not need a separate ternary (? :) operator.
When used as an expression, both the if and else branches are required.
The value of a branch is the value of its last expression/line.
Chains of else if are simply nested if-else expressions and can also return a value.

Practice what you learned

1. Why does Kotlin not have a ternary operator like Java's `? :`?

2. What is required when if-else is used as an expression (to produce a value)?

3. What value does a branch of an if-else expression evaluate to?

4. Which of the following is valid Kotlin code?

5. In the example, if `score` is 82, what would `grade` be?

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when Expression in Kotlin

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Introduction

Syntax

Explanation

Example

Key Takeaways

Practice what you learned

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