String charAt() Method

Java String charAt() returns the character located at the specified index in String. The string indexes start from zero and ranges from 0 to length() - 1. Syntax:
public char charAt(int index)
Example
class TestClass { public static void main (String[] args) { String str = "Halo World!"; System.out.println(str.charAt(0)); System.out.println(str.charAt(3)); System.out.println(str.charAt(9)); } }
Output
H o d
It is important to note that, it will thrown an IndexOutOfBoundsException if the index is less than zero or greater than equal to the length of the string (index<0|| index>=length()).

String Change to Uppercase

String toUpperCase()

Java String toUpperCase() converting the string to uppercase without needing to assign the result to a new variable. Example
class TestClass { public static void main (String[] args) { String str = "java string tutorial"; System.out.println(str.toUpperCase() ); } }

String Change to Lowecase

String toLowerCase()

Java String toLowerCase() converting the string to lowercase without needing to assign the result to a new variable. Example
class TestClass { public static void main (String[] args) { String str = "JAVA STRING TUTORIAL"; System.out.println(str.toLowerCase() ); } }