Kotlin How to Convert String to Uppercase Easily

In Kotlin, you can convert a string to uppercase by calling the uppercase() function on the string, like myString.uppercase().

Examples

Inputhello

OutputHELLO

InputKotlin is fun!

OutputKOTLIN IS FUN!

Input123abc

Output123ABC

How to Think About It

To convert a string to uppercase in Kotlin, think of changing every letter to its capital form. You use the built-in uppercase() function which goes through each character and makes it uppercase if it can. This is simple and direct.

Algorithm

1

Take the input string.

2

Call the uppercase function on the string.

3

Return the new string with all letters in uppercase.

Code

kotlin

fun main() {
    val original = "hello Kotlin"
    val uppercased = original.uppercase()
    println(uppercased)
}

Output

HELLO KOTLIN

Dry Run

Let's trace the string "hello Kotlin" through the code

1

Original string

original = "hello Kotlin"

2

Convert to uppercase

uppercased = original.uppercase() -> "HELLO KOTLIN"

3

Print result

Output: HELLO KOTLIN

Step	String Value
1	hello Kotlin
2	HELLO KOTLIN

Why This Works

Step 1: Using uppercase() function

The uppercase() function is built into Kotlin strings and converts all letters to uppercase.

Step 2: Returns new string

It does not change the original string but returns a new string with uppercase letters.

Alternative Approaches

uppercase(Locale)

kotlin

fun main() {
    val original = "hello Kotlin"
    val uppercased = original.uppercase(java.util.Locale.getDefault())
    println(uppercased)
}

Use this if you want to consider locale-specific uppercase rules.

Complexity: O(n) time, O(n) space

Time Complexity

The function processes each character once, so time grows linearly with string length.

Space Complexity

A new string is created to hold the uppercase result, so space also grows linearly.

Which Approach is Fastest?

Using uppercase() without locale is fastest for general use; locale-aware versions add slight overhead.

Approach	Time	Space	Best For
uppercase()	O(n)	O(n)	Simple uppercase conversion
uppercase(Locale)	O(n)	O(n)	Locale-specific uppercase rules