StringBuilder charAt() in Java

charAt(): This method is available in java.lang.AbstractStringBuilder class of Java.

Syntax:

char java.lang.AbstractStringBuilder.charAt(int index)

This method takes one argument of type int as a parameter. This method returns the char value in this sequence at the specified index.

Note: The index argument must be greater than or equal to 0, and less than the length of this sequence.

Parameters: One parameter is required for this method.

index: the index of the desired char value.

Returns: the char value at the specified index.

Throws:

StringIndexOutOfBoundsException - if index is negative or greater than or equal to length().

For Example:

StringBuilder str = new StringBuilder("Hello 123")

int index = 15

str.charAt(index) = > It returns l.

Approach 1: When the index is in the range.

Java

public class CharAt {
    public static void main(String[] args) {

        StringBuilder str = new StringBuilder("Hello 123");

        int index = 2;
        System.out.println(str.charAt(index));
    }
}

Output:

l

Approach 2: When the index is out of range.

Java

public class CharAt {
    public static void main(String[] args) {

        StringBuilder str = new StringBuilder("Hello 123");

        int index = 15;
        System.out.println(str.charAt(index));
    }
}

Output:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: index 15, length 9
	at java.base/java.lang.String.checkIndex(String.java:3693)
	at java.base/java.lang.AbstractStringBuilder.charAt(AbstractStringBuilder.java:351)
	at java.base/java.lang.StringBuilder.charAt(StringBuilder.java:85)