Java StringBuilder substring() Method

The StringBuilder.substring() method in Java is used to extract a substring from a StringBuilder object.

Table of Contents

1. Introduction
2. substring Method Syntax
3. Examples
   • Extracting a Substring
   • Extracting a Substring to the End
4. Real-World Use Case
5. Conclusion

Introduction

The StringBuilder.substring() method is a member of the StringBuilder class in Java. It allows you to extract a specific portion of the character sequence contained in the StringBuilder object. This method is useful when you need a part of the sequence as a new String object without modifying the original StringBuilder.

substring() Method Syntax

The StringBuilder class provides two overloaded substring methods:

1. substring(int start)
2. substring(int start, int end)

Method 1: substring(int start)

The syntax for extracting a substring from the specified start index to the end of the StringBuilder is as follows:

public String substring(int start)

• start: The beginning index, inclusive.

Method 2: substring(int start, int end)

The syntax for extracting a substring from the specified start index to the specified end index is as follows:

public String substring(int start, int end)

• start: The beginning index, inclusive.
• end: The ending index, exclusive.

Examples

Extracting a Substring

The substring method can be used to extract a substring within a specified range from a StringBuilder.

Example

public class StringBuilderSubstringExample {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("Hello, World!");

        // Extract a substring from index 7 to 12
        String subStr = sb.substring(7, 12);

        // Print the result
        System.out.println("Substring: " + subStr);
    }
}

Output:

Substring: World

Extracting a Substring to the End

You can also extract a substring from a specified start index to the end of the StringBuilder.

Example

public class StringBuilderSubstringExample {
    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder("Hello, World!");

        // Extract a substring from index 7 to the end
        String subStr = sb.substring(7);

        // Print the result
        System.out.println("Substring: " + subStr);
    }
}

Output:

Substring: World!

Real-World Use Case

Example: Extracting File Extensions

In a real-world scenario, you might need to extract the file extension from a file name. Using the substring method, you can locate the position of the last dot and extract the extension.

Example Code

public class FileExtensionExtractor {
    public static void main(String[] args) {
        StringBuilder fileName = new StringBuilder("example.document.txt");

        // Find the position of the last dot
        int lastDotIndex = fileName.lastIndexOf(".");

        // Extract the file extension
        String fileExtension = fileName.substring(lastDotIndex + 1);

        // Print the file extension
        System.out.println("File extension: " + fileExtension);
    }
}

Output:

File extension: txt

Conclusion

The StringBuilder.substring() method in Java is used for extracting substrings from a StringBuilder object. By understanding how to use the overloaded methods, you can efficiently extract specific portions of a character sequence as new String objects. Whether you need to extract a substring within a specified range or from a start index to the end, the substring method provides a reliable solution for these tasks.