Strings in Kotlin

# CHAPTER 11

Strings in Kotlin #

1. Chapter Introduction #

2. Learning Objectives #

• Access individual characters in a String.

• Use built-in String methods (length, uppercase, substring).

• Compare strings securely.

• Create multi-line "Raw Strings" using triple quotes.

3. Strings are Immutable #

4. Basic String Operations #

fun main() {
    val message = "Kotlin"

    // Getting the length (Number of characters)
    println("Length: ${message.length}") // 6

    // Accessing individual characters by index
    println("First letter: ${message[0]}") // K
    println("Last letter: ${message[5]}")  // n
    
    // Iterating over a string
    for (char in message) {
        print("$char ") // K o t l i n 
    }
}

5. Essential String Methods #

fun main() {
    val text = "  Learn Kotlin Today  "

    // Removing whitespace from the beginning and end
    val cleanText = text.trim() 
    println("Trimmed: '$cleanText'") // 'Learn Kotlin Today'

    // Case conversion
    println(cleanText.uppercase()) // LEARN KOTLIN TODAY
    println(cleanText.lowercase()) // learn kotlin today

    // Searching inside a string
    println(cleanText.contains("Kotlin")) // true
    println(cleanText.startsWith("Learn")) // true

    // Replacing text
    val newText = cleanText.replace("Today", "Tomorrow")
    println(newText) // Learn Kotlin Tomorrow

    // Substrings (Extracting a portion)
    val word = cleanText.substring(6, 12) // Extracts from index 6 up to 11
    println("Extracted: $word") // Kotlin
}

6. String Comparison #

fun main() {
    val pass1 = "Secret123"
    val pass2 = "secret123"

    println(pass1 == pass2) // false (case sensitive)
    
    // Ignore case
    println(pass1.equals(pass2, ignoreCase = true)) // true
}

7. Raw Strings (Triple Quotes) #

fun main() {
    // A multiline raw string
    val sqlQuery = """
        SELECT * FROM users
        WHERE age > 18
        AND status = 'ACTIVE'
    """.trimIndent() // Removes the leading indentation for a clean print!

    println(sqlQuery)
}

8. Common Mistakes #

• IndexOutOfBounds: Remember that Strings are 0-indexed. If a string has a length of 5, the maximum index is 4. Trying to access str[5] will crash the program.

• Forgetting Reassignment: Because Strings are immutable, writing text.trim() does nothing to the original variable. You must assign the result to a new variable: val cleaned = text.trim().

9. Best Practices #

• Use .trimIndent(): Whenever you use a multiline Raw String ("""), append .trimIndent(). This allows you to indent the string in your code to make it look pretty, without actually printing those huge blocks of blank space to the console.

10. Exercises #

1. 1. Create a variable password = " P@ssw0rd ".

1. 2. Create a new variable cleanPass by trimming the whitespace.

1. 3. Check if cleanPass contains the @ symbol and print the boolean result.

1. 4. Print the cleanPass in all uppercase.

11. MCQs with Answers #

12. Interview Questions #

• Q: What does it mean that Strings are "Immutable"? Why is this good for memory? (Answer: Once created, they cannot be changed. This allows the JVM to safely reuse string instances in a "String Pool" without worrying that one part of the app will secretly alter the string for another part).

• Q: Explain how Kotlin handles String equality (==) compared to Java.

13. Summary #

14. Next Chapter Recommendation #