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StringBuilder charAt() in Java with Examples

Last Updated : 15 Oct, 2018
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The charAt(int index) method of StringBuilder Class is used to return the character at the specified index of String contained by StringBuilder Object. The index value should lie between 0 and length()-1. Syntax: 
public char charAt(int index)
Parameters: This method accepts one int type parameter index which represents index of the character to be returned. Return Value: This method returns character at the specified position. Exception: This method throws IndexOutOfBoundsException when index is negative or greater than or equal to length(). Below programs demonstrate the charAt() method of StringBuilder Class: Example 1: Java 
// Java program to demonstrate
// the charAt() Method.

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

        // create a StringBuilder object
        StringBuilder str = new StringBuilder();

        // add the String to StringBuilder Object
        str.append("Geek");

        // get char at position 1
        char ch = str.charAt(1);

        // print the result
        System.out.println("StringBuilder Object"
                           + " contains = " + str);
        System.out.println("Character at Position 1"
                           + " in StringBuilder = " + ch);
    }
}
Output: 
StringBuilder Object contains = Geek
Character at Position 1 in StringBuilder = e
Example 2: Java 
// Java program demonstrate
// the charAt() Method.

class GFG {
    public static void main(String[] args)
    {
        // create a StringBuilder object
        // with a String pass as parameter
        StringBuilder
            str
            = new StringBuilder("WelcomeGeeks");

        // print string
        System.out.println("String is "
                           + str.toString());

        // loop through string and print every Character
        for (int i = 0; i < str.length(); i++) {

            // get char at position i
            char ch = str.charAt(i);

            // print char
            System.out.println("Char at position "
                               + i + " is " + ch);
        }
    }
}
Output: 
String is WelcomeGeeks
Char at position 0 is W
Char at position 1 is e
Char at position 2 is l
Char at position 3 is c
Char at position 4 is o
Char at position 5 is m
Char at position 6 is e
Char at position 7 is G
Char at position 8 is e
Char at position 9 is e
Char at position 10 is k
Char at position 11 is s
Example 3: To demonstrate IndexOutOfBoundException Java 
// Java program to demonstrate
// IndexOutOfBound exception thrown by the charAt() Method.

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

        try {

            // create a StringBuilder object
            // with a String pass as parameter
            StringBuilder
                str
                = new StringBuilder("WelcomeGeeks");

            // get char at position i
            char ch = str.charAt(str.length());

            // print char
            System.out.println("Char at position "
                               + str.length() + " is "
                               + ch);
        }

        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}
Output: 
Exception: java.lang.StringIndexOutOfBoundsException:
 String index out of range: 12
Reference: https://docs.oracle.com/javase/10/docs/api/java/lang/StringBuilder.html#charAt(int)

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