Uppercase and Lowercase in Java

In Java, String objects have built-in methods to change their case:

s.toUpperCase()   // converts all characters to uppercase
s.toLowerCase()   // converts all characters to lowercase

Here are some examples:

String word = "Hello World";
String upper = word.toUpperCase();  // "HELLO WORLD"
String lower = word.toLowerCase();  // "hello world"

String name = "ALICE";
System.out.println(name.toLowerCase());  // "alice"

These methods return a new String — the original is not modified.