Kotlin String substring

The substring function in Kotlin is used to extract a part of a string. This function is part of the Kotlin standard library and provides a straightforward way to get a substring from a given string.

Table of Contents

1. Introduction
2. substring Function Syntax
3. Examples
   • Basic Usage
   • Using substring with Start and End Index
   • Handling Index Out of Bounds
4. Real-World Use Case
5. Conclusion

Introduction

The substring function extracts a part of a string, specified by a range of indices. This is useful for tasks such as parsing, extracting, and manipulating portions of a string.

The substring function can be used in two ways:

1. Extracting a substring from a starting index to the end of the string.
2. Extracting a substring from a starting index to an ending index.

substring Function Syntax

The syntax for the substring function is as follows:

fun String.substring(startIndex: Int): String
fun String.substring(startIndex: Int, endIndex: Int): String

Parameters:

• startIndex: The starting index (inclusive) of the substring.
• endIndex: The ending index (exclusive) of the substring (optional).

Returns:

• A new string containing the characters from the specified range of the original string.

Throws:

• IndexOutOfBoundsException if the start or end index is out of bounds.

Examples

Basic Usage

To demonstrate the basic usage of substring, we will create a string and extract substrings from it.

Example

fun main() {
    val text = "Hello, World!"
    val subText1 = text.substring(7)
    val subText2 = text.substring(0, 5)

    println("Original text: $text")
    println("Substring from index 7: $subText1")
    println("Substring from index 0 to 5: $subText2")
}

Output:

Original text: Hello, World!
Substring from index 7: World!
Substring from index 0 to 5: Hello

Using substring with Start and End Index

This example shows how to use substring with both a start and end index to extract a specific portion of a string.

Example

fun main() {
    val text = "Kotlin Programming"
    val subText = text.substring(7, 18)

    println("Original text: $text")
    println("Substring from index 7 to 18: $subText")
}

Output:

Original text: Kotlin Programming
Substring from index 7 to 18: Programming

Handling Index Out of Bounds

This example demonstrates how to handle cases where the indices are out of bounds.

Example

fun main() {
    val text = "Kotlin"
    try {
        val subText = text.substring(3, 10)
        println("Substring from index 3 to 10: $subText")
    } catch (e: IndexOutOfBoundsException) {
        println("Error: ${e.message}")
    }
}

Output:

Error: String index out of range: 10

Real-World Use Case

Extracting a Domain from an Email

In real-world applications, the substring function can be used to extract specific parts of a string, such as extracting the domain from an email address.

Example

fun main() {
    val email = "user@example.com"
    val atIndex = email.indexOf('@')
    val domain = email.substring(atIndex + 1)

    println("Email: $email")
    println("Domain: $domain")
}

Output:

Email: user@example.com
Domain: example.com

Conclusion

The substring function in Kotlin is a convenient method for extracting parts of a string. It provides a simple way to manipulate and handle substrings based on specified indices. 

By understanding and using this function, you can effectively manage string extraction and manipulation operations in your Kotlin applications.