Java .substring()

The .substring() method in Java returns a portion of a string from a specified starting index to an (optional) ending index. If an ending index is not provided, the substring extends from the starting index to the end of the original string.

This method is commonly used for text processing, data parsing, and string manipulation tasks. It offers two variants that allow the extraction of characters either from a specific starting index or between a range of indices.

Syntax

string.substring(startIndex);
string.substring(startIndex, endIndex);

• .substring() returns characters from startIndex up to, but does not include, the character at endIndex.
• If endIndex is omitted, .substring() returns characters from startIndex to the end of the string.
• If startIndex and endIndex are equal, .substring() returns an empty string.

A StringIndexOutOfBoundsException is thrown if any of the following are true:

• startIndex is greater than endIndex
• startIndex is greater than the length of the original string
• startIndex or endIndex is negative

Example 1: Extracting Characters From a Specific Index to the End

This example demonstrates how to extract a substring using substring(beginIndex) method, starting from a specific index to the end of the string:

class Main {

  public static void main(String[] args) {

    String text = "Hello, Java!";

    String result = text.substring(7);

    System.out.println("Original string: " + text);

    System.out.println("Substring starting from index 7: " + result);

  }
}

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This example results in the following output:

Original string: Hello, Java!
Substring starting from index 7: Java!

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In this example, substring(7) extracts all characters from index 7 (inclusive) to the end of the string.

Example 2: Extracting Characters Between Two Indices

This example demonstrates how to extract a substring using substring(beginIndex, endIndex) method between a specific range of indices:

class Main {

  public static void main(String[] args) {

    String text = "Programming with Java";

    String result = text.substring(0, 11);

    System.out.println("Original string: " + text);

    System.out.println("Substring from index 0 to 11: " + result);

  }
}

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This example results in the following output:

Original string: Programming with Java
Substring from index 0 to 11: Programming

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In this example, substring(0, 11) extracts characters from index 0 (inclusive) to index 11 (exclusive).

Frequently Asked Questions

1. Does a substring start at 0 in Java?

Yes, string indexing in Java starts at 0, so the first character of a string is at index 0. When using the substring() method, the beginIndex parameter follows this zero-based indexing.

2. Is a substring in Java inclusive?

The beginIndex parameter in the substring() method is inclusive, meaning the character at that index will be included in the result. However, the endIndex parameter is exclusive, meaning the character at that index will not be included in the result.

3. Is an empty string a substring?

Yes, an empty string is a valid substring in Java. You can get an empty string by:

• Using the same value for both beginIndex and endIndex in substring(beginIndex, endIndex)
• Using substring(str.length()), which returns an empty string since it starts at the end of the string