Convert a String to lowercase or uppercase

The following example is self-explanatory:

public class TestProg
    public static void main(String args[])
        String s = "Hello, World!";
        String supper = s.toUpperCase();
        String slower = s.toLowerCase();
        System.out.println(supper);    // prints out: HELLO, WORLD!
        System.out.println(slower);    // prints out: hello, world!

Note: for internationalization purposes, the methods toUpperCase() and toLowerCase() perform some checking for languages as German and Turkish to do the correct conversion.
If you need these functions in time-critical applications, you might want to consider rewriting them without these checkings.