Kotlin:
Converting a string to lower case

How to:

Kotlin’s toLowerCase() function turns all characters in a string to lower case quickly. Here’s how you use it:

fun main() {
    val originalString = "ThiS iS A MixED cAsE String!"
    val lowerCaseString = originalString.lowercase()

    println(lowerCaseString) // Output: this is a mixed case string!
}

Invoke lowercase() and you’re done. Input caps don’t matter; output’s all lower case.

Deep Dive

Kotlin didn’t reinvent the wheel for lower-casing strings. It’s actually a common feature across programming languages. Historically, functions like C’s tolower() have long dealt with case conversion.

Now, two twists when lowercasing: locales and performance. Kotlin’s lowercase() can accept a Locale because, surprise, character casing isn’t universal. For instance, the Turkish dotted and dotless ‘I’ behave uniquely in case conversions.

Performance? In most apps, you won’t notice. But large-scale text processing hogs more memory and time because strings in Kotlin are immutable. When you lowercase a string, you get a new string.

Old-schoolers remember .toLowerCase() — Kotlin now prefers lowercase() for clarity.

See Also

• Kotlin String Documentation: Kotlinlang.org
• For text processing and advanced case manipulation, check the java.lang.String API: Oracle Docs
• Understanding locales and language quirks: Oracle Locale Docs