StringBuilder charAt() in Java with Examples

15 Oct, 2018
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);    }}
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);        }    }}
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);        }    }}
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)
java-basics
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