Need help with StringBuffer

[vicml21]

code:

public class Lab10Exc2 {     // reverse a string     public static StringBuffer reverse (String src)     {         StringBuffer str = new StringBuffer ();         for (int k = (src.length () - 1) ; k >= 0 ; k--)         {             str.append (src.charAt (k));         }         return str;     }     public static void main (String argv[])     {         StringBuffer message = "Today is a sunny day!";         StringBuffer reversed = reverse (message);         System.out.println ("The reverse of: " + message + " is: " + reversed);     } }

ok im not really sure how StringBuffers work, but what this program is supposed to do is get the text "Today is a sunny day!" and reverse it using StringBuffers & for loops