String type and immutability in Kotlin

Introduction

Strings hold text in programs. They cannot be changed once created, which helps avoid mistakes.

When you want to store names or messages in your app.

When you need to compare or search text.

When you want to build text step-by-step safely.

When you want to pass text data between parts of your program.

When you want to keep text data safe from accidental changes.

Syntax

Kotlin

val text: String = "Hello, Kotlin!"

val means the string cannot be reassigned to a new value.

Strings are immutable, so you cannot change characters inside once created.

Examples

Create a string with text "Hi!" and store it in greeting.

Kotlin

val greeting: String = "Hi!"

Kotlin can guess the type String, so you can skip writing it.

Kotlin

val name = "Alice"

Combine two strings using + to make a new string.

Kotlin

val combined = greeting + " " + name

Get the number of characters in the string using length property.

Kotlin

val length = name.length

Sample Program

This program shows that you cannot change a character inside a string. Instead, you create a new string by adding text.

Kotlin

fun main() {
    val original = "Hello"
    // Try to change a character (not allowed)
    // original[0] = 'J' // This line would cause an error

    val newString = original + ", Kotlin!"
    println("Original string: $original")
    println("New string: $newString")
}

Important Notes

Strings are immutable, so any change creates a new string.

Use val to keep string references constant, but var can point to new strings.

To build text efficiently in loops, use StringBuilder instead of repeated string concatenation.

Summary

Strings hold text and cannot be changed once created.

Use + to combine strings and create new ones.

Immutability helps keep your text data safe and predictable.