Answer:
public class TextConverterDemo
{
//Method definition of action1337
public static String action1337(String current)
{
//Replace each L or l with a 1 (numeral one)
  current = current.replace('L', '1');
  current = current.replace('l', '1');
  
  //Replace each E or e with a 3 (numeral three)
  current = current.replace('E', '3');
  current = current.replace('e', '3');
  //Replace each T or t with a 7 (numeral seven)
  current = current.replace('T', '7');
  current = current.replace('t', '7');
  //Replace each O or o with a 0 (numeral zero)
  current = current.replace('O', '0');
  current = current.replace('o', '0');
  
//Replace each S or s with a $ (dollar sign)
  current = current.replace('S', '$');
  current = current.replace('s', '$');
  return current;
}
//Method definition of actionReverse
//This method is used to reverses the order of
//characters in the current string
public static String actionReverse(String current)
{
  //Create a StringBuilder's object
  StringBuilder originalStr = new StringBuilder();
  //Append the original string to the StribgBuilder's object
  originalStr.append(current);
  //Use reverse method to reverse the original string
  originalStr = originalStr.reverse();
  
  //return the string in reversed order
  return originalStr.toString();
}
//Method definition of main
public static void main(String[] args)
{
     //Declare variables
  String input, action;
  
  //Prompt the input message
  System.out.println("Welcome to the Text Converter.");
  System.out.println("Available Actions:");
  System.out.println("\t1337) convert to 1337-speak");
  System.out.println("\trev) reverse the string");
  System.out.print("Please enter a string: ");
    
  //Create a Scanner class's object
  Scanner scn = new Scanner(System.in);
  
  //Read input from the user
  input = scn.nextLine();
  do
  {
   /*Based on the action the user chooses, call the appropriate
    * action method. If an unrecognized action is entered then
    * the message "Unrecognized action." should be shown on a
    * line by itself and then the user is prompted again just
    * as they were when an action was performed.
    * */
   System.out.print("Action (1337, rev, quit): ");
   action = scn.nextLine();
   if (action.equals("1337"))
   {
    input = action1337(input);
    System.out.println(input);
   } else if (action.equals("rev"))
   {
    input = actionReverse(input);
    System.out.println(input);
   } else if (!action.equals("quit"))
   {
    System.out.println("Unrecognized action.");
   }
  } while (!action.equals("quit"));
  System.out.println("See you next time!");
  scn.close();
}
}