String methods

Learn uppercase, lowercase and trim methods.

uppercase, lowercase, trim

To change case in Strings, use uppercase() and lowercase(). To strip leading and trailing spaces, call trim().

val s = "Hello"
println(s.uppercase())  // HELLO
println(s.lowercase())  // hello
val t = "  Alex  "
println(t.trim())      // Alex

These methods return a new String; the original is unchanged (Strings are immutable). So you must assign the result or use it directly.

Locale-specific characters are handled: "été".uppercase() gives "ÉTÉ".

Exercise Use trim and uppercase

Write a fun main(). Assign " Alex " (spaces at both ends) to val s. Print s.trim() and s.trim().uppercase() on separate lines.

Show example solution

fun main() {
    val s = "  Alex  "
    println(s.trim())
    println(s.trim().uppercase())
}

Method chaining

Multiple methods can be called back to back on a String; this is called chaining. Each call returns a String, so the next method applies to that result.

val s = "  Hello  "
val r = s.trim().uppercase()
println(r)  // HELLO

It runs left to right: first trim() cuts spaces, then uppercase() makes it capital. Order matters; uppercase().trim() may give a different result.

Chaining keeps code short and readable; no intermediate variables needed.

Test yourself

What does "hello".uppercase() return?
- hello
- Error
- Hello
- HELLO
Show answer

HELLO — uppercase turns all letters to capitals: HELLO.

Complete the uppercase call

val up = name.____()

Show answer

val up = name.uppercase()

Match the methods

uppercase()

Makes capitals
lowercase()

Makes small
trim()

Cuts spaces
trim().uppercase()

Clean and capitalize

Next lesson: substring

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