Java String substring() method

The substring() method in Java is used to extract a portion (sub-string) of a string. It belongs to the String class and allows you to create a new string by selecting a part of an existing string.

Parameters in Method

1. String substring(int beginIndex)

This method returns a new string that starts from the specified beginIndex to the end of the string.

Example:

public class SubstringSingleParameterExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        // Extract substring from index 7 to the end of the string
        String subStr1 = str.substring(7);
        System.out.println(subStr1);  // Output: World!
    }
}

Explanation: substring(7) starts at index 7 and returns the substring from there to the end of the string: “World!”

2. substring(int beginIndex, int endIndex)

The method returns a new String object that contains the characters from the original string, starting from the beginIndex (inclusive) and optionally up to endIndex (exclusive).

Example:

public class SubstringTwoParametersExample {
    public static void main(String[] args) {
        String str = "Hello, World!";
        
        // Extract substring from index 0 to index 5 (exclusive)
        String subStr2 = str.substring(0, 5);
        System.out.println(subStr2);  // Output: Hello
    }
}

Explanation: In this example, substring(0, 5) extracts the substring starting at index 0 and ending at index 4, which gives the substring “Hello”.

3. Handle Invalid Index

public class SubstringExample {
    public static void main(String[] args) {
        String str = "Hello World!";
        
        try {
            String subStr = str.substring(15, 5);
        } catch (StringIndexOutOfBoundsException e) {
            System.out.println("Error: " + e.getMessage());  // Output: String index out of range: 15 to 5
        }
    }
}

Explanation: Here, attempting to extract a substring where the beginIndex (15) is greater than endIndex (5) throws a StringIndexOutOfBoundsException.