Kotlin Variables Unveiled: Understanding var, val, and Naming Best Practices

Variables are containers for storing data values—and in Kotlin, they’re a breeze to master! 🚀

In 2025, Kotlin remains a standout language for its sleek, intuitive variable handling. Whether you’re a newbie or a pro, variables are your gateway to Kotlin’s magic. Let’s explore every angle of Kotlin variables with flair! 🌟

• ✨ Create variables effortlessly with var or val, assigning values using the equal sign (=).
• 🔄 var variables are flexible and can be updated anytime, while val locks in a value for good—no changes allowed! 🔒
• 🧠 Kotlin’s type inference skips the need for explicit types, making your code cleaner and faster to write.

Last updated : March 3rd 2025

Type Magic: No Guesswork Needed! 🪄

Kotlin doesn’t demand you declare types like "String" or "Int"—it’s smart enough to detect them automatically:

var name = "John"      // String (text)
val birthyear = 1992   // Int (number)
var price = 19.99    // Double (decimal)

From "John" as a String to 19.99 as a Double, Kotlin’s got it covered without extra typing! 🎉

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Delayed Assignment? Specify the Type! ⏳

You can declare a variable now and assign it later, but you’ll need to tell Kotlin the type upfront:

var name: String
name = "John"
println(name)  // Outputs: John
var age: Int = 25  // Optional: assign at declaration

Pro Tip: Uninitialized var variables must be assigned before use, or Kotlin will throw an error! ⚠️

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When to Use val? Lock It In! 🔐

val is your best friend for constants—values that stay put, like PI or app settings:

val PI = 3.14159  // Forever 3.14159
val appVersion = "1.0.0"  // No updates here!

Attempting to reassign a val? Kotlin says, “Nope!”—perfect for safety. 🚫

Everything You Need to Know About Kotlin Variables: 📜

• 📏 Short or Sweet Names: Use x or y for quick tasks, or userAge, totalSum, maxVolume for clarity.
• 🔡 Allowed Characters: Letters, digits, underscores (_), and dollar signs ($) are fair game.
• 🚦 Start Right: Begin with a letter—numbers or symbols won’t fly.
• 💡 Special Starts: $ or _ are okay (e.g., $price), but we’ll skip them in this guide.
• 👀 Case Sensitivity: myVar and myvar are different—watch those capitals!
• 📝 Lowercase Start: Begin with lowercase (e.g., firstName), and no whitespace allowed.
• 🚫 No Reserved Words: Keywords like var, val, or String are off-limits as names.
• 🐪 CamelCase FTW: Combine words with capitals (e.g., myFavoriteColor, calculateTotalScore).
• 🌍 Scope Matters: Variables live where you declare them—inside a function (local) or outside (global).
• ⏲️ Late Initialization: Use lateinit var for non-null variables you’ll assign later (but only for var, not val!).
• 🔢 Common Types: Beyond String and Int, try Double, Float, Boolean (true/false), and more.
• ⚡ Reassignment Rules: Change a var anytime, but its type stays fixed (e.g., no turning an Int into a String).

Why CamelCase Rocks: We used firstName and lastName instead of firstname or lastname. This camelCase style splits words with capitals, making names like myFavoriteFood or trackDailySteps a joy to read! 😍

Scope in Action: Where you place a variable defines its reach:

val globalLimit = 100  // Accessible everywhere
fun testScope() {
    var localCount = 5  // Only lives here
}

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