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 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 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 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)
