Kotlin Strings

String Features

val text = "Hello"

val full = "Hello" + " World"

val msg = "Hi, $name!"

val len = text.length

🔹 Creating Strings

Different ways to create and define strings:

// Basic string creation
val simpleString = "Hello, Kotlin!"
val emptyString = ""
val singleChar = "A"

// Escape sequences
val withQuotes = "She said, \"Hello!\""
val withNewline = "Line 1\nLine 2"
val withTab = "Name:\tJohn"
val withBackslash = "Path: C:\\Users\\John"

// Raw strings (triple quotes)
val rawString = """
    This is a raw string.
    It can contain "quotes" and \backslashes
    without escaping them.
    Newlines are preserved.
""".trimIndent()

// String from other types
val number = 42
val numberString = number.toString()    // "42"
val boolString = true.toString()        // "true"

🔹 String Interpolation

Embed variables and expressions directly in strings:

val firstName = "John"
val lastName = "Doe"
val age = 30
val salary = 50000.0

// Simple variable interpolation
val greeting = "Hello, $firstName!"
val fullName = "Full name: $firstName $lastName"

// Expression interpolation with curly braces
val info = "Name: ${firstName.uppercase()}, Age: $age"
val calculation = "Next year I'll be ${age + 1} years old"
val formatted = "Salary: $${String.format("%.2f", salary)}"

// Complex expressions
val status = "Status: ${if (age >= 18) "Adult" else "Minor"}"
val summary = """
    Employee Summary:
    - Name: $firstName $lastName
    - Age: $age years
    - Salary: $$salary
    - Category: ${if (salary > 40000) "High earner" else "Standard"}
""".trimIndent()

🔹 String Operations

Common operations you can perform on strings:

val text = "  Hello, Kotlin World!  "

// Length and access
val length = text.length                    // 23
val firstChar = text[2]                     // 'H' (index 2, after spaces)
val lastChar = text[text.length - 1]       // ' ' (last space)

// Case operations
val upperCase = text.uppercase()            // "  HELLO, KOTLIN WORLD!  "
val lowerCase = text.lowercase()            // "  hello, kotlin world!  "

// Trimming whitespace
val trimmed = text.trim()                   // "Hello, Kotlin World!"
val trimStart = text.trimStart()           // "Hello, Kotlin World!  "
val trimEnd = text.trimEnd()               // "  Hello, Kotlin World!"

// Substring operations
val substring = text.substring(2, 7)        // "Hello"
val substringFrom = text.substring(8)       // "Kotlin World!  "

// Searching
val contains = text.contains("Kotlin")      // true
val startsWith = text.trim().startsWith("Hello")  // true
val endsWith = text.trim().endsWith("!")   // true
val indexOf = text.indexOf("Kotlin")       // 8

🔹 String Splitting and Joining

Break strings apart and combine them:

// Splitting strings
val csvData = "apple,banana,orange,grape"
val fruits = csvData.split(",")             // ["apple", "banana", "orange", "grape"]

val sentence = "The quick brown fox"
val words = sentence.split(" ")             // ["The", "quick", "brown", "fox"]

val email = "[email protected]"
val emailParts = email.split("@")           // ["user", "example.com"]

// Joining strings
val fruitList = listOf("apple", "banana", "orange")
val joined = fruitList.joinToString(", ")   // "apple, banana, orange"
val withAnd = fruitList.joinToString(" and ")  // "apple and banana and orange"

// Custom separators and formatting
val numbers = listOf(1, 2, 3, 4, 5)
val formatted = numbers.joinToString(
    separator = " | ",
    prefix = "[",
    postfix = "]"
)  // "[1 | 2 | 3 | 4 | 5]"

🔹 String Replacement

Replace parts of strings with new content:

val originalText = "I love Java programming. Java is great!"

// Replace first occurrence
val replaceFirst = originalText.replaceFirst("Java", "Kotlin")
// "I love Kotlin programming. Java is great!"

// Replace all occurrences
val replaceAll = originalText.replace("Java", "Kotlin")
// "I love Kotlin programming. Kotlin is great!"

// Replace with different cases
val mixedCase = "Hello WORLD hello world"
val replaced = mixedCase.replace("hello", "hi", ignoreCase = true)
// "hi WORLD hi world"

// Remove characters
val withSpaces = "H e l l o   W o r l d"
val noSpaces = withSpaces.replace(" ", "")      // "HelloWorld"

// Replace multiple characters
val phoneNumber = "(555) 123-4567"
val cleanNumber = phoneNumber.replace(Regex("[()\\s-]"), "")  // "5551234567"