Java StringBuilder indexOf() Method

The StringBuilder.indexOf() method in Java is used to find the index of the first occurrence of a specified substring within a StringBuilder object. This guide will cover the method’s usage, explain how it works, and provide examples to demonstrate its functionality, including the overloaded methods.

Table of Contents

1. Introduction
2. indexOf Method Syntax
3. Examples
   • Finding the Index of a Substring
   • Finding the Index of a Substring from a Specified Position
4. Real-World Use Case
5. Conclusion

Introduction

The StringBuilder.indexOf() method is a member of the StringBuilder class in Java. It allows you to search for the first occurrence of a specified substring within the StringBuilder object. This method is particularly useful when you need to locate specific substrings within a mutable sequence of characters.

indexOf() Method Syntax

The StringBuilder class provides two overloaded indexOf methods:

1. indexOf(String str)
2. indexOf(String str, int fromIndex)

Method 1: indexOf(String str)

The syntax for the first indexOf method is as follows:

public int indexOf(String str)

• str: The substring to search for.

Method 2: indexOf(String str, int fromIndex)

The syntax for the second indexOf method is as follows:

public int indexOf(String str, int fromIndex)

• str: The substring to search for.
• fromIndex: The index to start the search from.

Examples

Finding the Index of a Substring

The first indexOf method can be used to find the index of the first occurrence of a specified substring within a StringBuilder.

Example

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

        // Find the index of the substring "World"
        int index = sb.indexOf("World");

        // Print the index
        System.out.println("Index of 'World': " + index);
    }
}

Output:

Index of 'World': 7

Finding the Index of a Substring from a Specified Position

The second indexOf method can be used to find the index of the first occurrence of a specified substring, starting the search from a given index.

Example

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

        // Find the index of the substring "World" starting from index 10
        int index = sb.indexOf("World", 10);

        // Print the index
        System.out.println("Index of 'World' after position 10: " + index);
    }
}

Output:

Index of 'World' after position 10: 20

In this example, the search for the substring "World" starts from index 10, and it finds the second occurrence of "World" in the string.

Real-World Use Case

Example: Parsing a CSV String

In a real-world scenario, you might need to parse a CSV (Comma-Separated Values) string to extract specific fields. Using the indexOf method, you can locate the positions of commas and extract the desired fields efficiently.

Example Code

public class CSVParser {
    public static void main(String[] args) {
        StringBuilder csv = new StringBuilder("John,Doe,30,Male,Software Engineer");

        // Find the index of the first comma
        int firstComma = csv.indexOf(",");
        // Find the index of the second comma
        int secondComma = csv.indexOf(",", firstComma + 1);

        // Extract the first and second fields
        String firstName = csv.substring(0, firstComma);
        String lastName = csv.substring(firstComma + 1, secondComma);

        // Print the extracted fields
        System.out.println("First Name: " + firstName);
        System.out.println("Last Name: " + lastName);
    }
}

Output:

First Name: John
Last Name: Doe

Conclusion

The StringBuilder.indexOf() method in Java is used for locating substrings within a StringBuilder object. By understanding how to use the overloaded methods, you can efficiently search for substrings either from the beginning of the StringBuilder or from a specified position. Whether you need to find the index of a substring or start the search from a particular index, the indexOf methods provide a reliable solution for these tasks.