Java String offsetByCodePoints() Method

The String.offsetByCodePoints() method in Java is used to find the index within a string that is offset by a given number of code points from a specified index. This guide will cover the method's usage, explain how it works, and provide examples to demonstrate its functionality.

Table of Contents

1. Introduction
2. offsetByCodePoints Method Syntax
3. Examples
   • Basic Usage
   • Handling Supplementary Characters
4. Conclusion

Introduction

The String.offsetByCodePoints() method is a member of the String class in Java. It allows you to find the index within a string that is offset by a specified number of code points from a given index. This is particularly useful when dealing with strings that contain supplementary characters.

offsetByCodePoints Method Syntax

The syntax for the offsetByCodePoints method is as follows:

public int offsetByCodePoints(int index, int codePointOffset)

• index: The starting index.
• codePointOffset: The number of code points to offset from the starting index.

Examples

Basic Usage

The offsetByCodePoints method can be used to find the index within a string that is offset by a specified number of code points from a given index.

Example

public class OffsetByCodePointsExample {
    public static void main(String[] args) {
        String str = "Hello, World!";

        int offsetIndex = str.offsetByCodePoints(0, 7);

        System.out.println("Original string: " + str);
        System.out.println("Offset index: " + offsetIndex);
        System.out.println("Character at offset index: " + str.charAt(offsetIndex));
    }
}

Output:

Original string: Hello, World!
Offset index: 7
Character at offset index: W

Handling Supplementary Characters

The offsetByCodePoints method correctly handles supplementary characters, which are represented by a pair of char values (a surrogate pair) in UTF-16.

Example

public class OffsetByCodePointsExample {
    public static void main(String[] args) {
        String str = "a\uD835\uDD0Ab";  // 'a' followed by a supplementary character and 'b'

        int offsetIndex = str.offsetByCodePoints(0, 2);

        System.out.println("Original string: " + str);
        System.out.println("Offset index: " + offsetIndex);
        System.out.println("Character at offset index: " + str.charAt(offsetIndex));
    }
}

Output:

Original string: a𝒊b
Offset index: 3
Character at offset index: b

Handling Edge Cases

The offsetByCodePoints method will throw IndexOutOfBoundsException if the specified index or the resulting index is out of range.

Example

public class OffsetByCodePointsExample {
    public static void main(String[] args) {
        String str = "Hello, World!";

        try {
            int offsetIndex = str.offsetByCodePoints(0, 20);
            System.out.println("Offset index: " + offsetIndex);
        } catch (IndexOutOfBoundsException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

Output:

Error: String index out of range: 20

Conclusion

The String.offsetByCodePoints() method in Java is used for finding the index within a string that is offset by a specified number of code points from a given index. By understanding how to use this method, you can efficiently handle strings that contain supplementary characters in your Java applications. Whether you are working with basic strings or dealing with edge cases, the offsetByCodePoints method provides a reliable solution for these tasks.