Telephone Digits - Java Sample Program

/*
The following program reads the letter codes 'A' through 'Z' and prints the corresponding
telephone digit. This program uses a sentinel-controlled while loop. To stop
the program, the user is prompted for the sentinel, which is '#'. This is also an example
of a nested control structure, where if... else, switch, and the while loop are
nested.
*/

//********************************************************
// Program: Telephone Digits
// This is an example of a sentinel-controlled while loop.
// This program converts uppercase letters to their
// corresponding telephone digits.
// Filename: TelephoneDigitProgram.java
//********************************************************

import javax.swing.JOptionPane;
public class TelephoneDigitProgram
{
public static void main (String[] args)
{
char letter; //Line 1
String inputMessage; //Line 2
String inputString; //Line 3
String outputMessage; //Line 4

inputMessage = "Program to convert uppercase "
+ "letters to their corresponding "
+ "telephone digits.\n"
+ "To stop the program enter #.\n"
+ "Enter a letter:"; //Line 5

inputString = JOptionPane.showInputDialog(inputMessage); //Line 6
letter = inputString.charAt(0); //Line 7

while (letter != '#' ) //Line 8
{
outputMessage = "The letter you entered is: "
+ letter + "\n"
+ "The corresponding telephone "
+ "digit is: "; //Line 9

if (letter >= 'A' && letter <= 'Z') //Line 10
{
switch (letter) //Line 11
{
case 'A':
case 'B':
case 'C': outputMessage = outputMessage + "2"; //Line 12
break; //Line 13
case 'D':
case 'E':
case 'F': outputMessage = outputMessage + "3"; //Line 14
break; //Line 15
case 'G':
case 'H':
case 'I': outputMessage = outputMessage + "4"; //Line 16
break; //Line 17
case 'J':
case 'K':
case 'L': outputMessage = outputMessage + "5"; //Line 18
break; //Line 19
case 'M':
case 'N':
case 'O': outputMessage = outputMessage + "6"; //Line 20
break; //Line 21
case 'P':
case 'Q':
case 'R':
case 'S': outputMessage = outputMessage + "7"; //Line 22
break; //Line 23
case 'T':
case 'U':
case 'V': outputMessage = outputMessage + "8"; //Line 24
break; //Line 25
case 'W':
case 'X':
case 'Y':
case 'Z': outputMessage = outputMessage + "9"; //Line 26
}
}
else //Line 27
outputMessage = outputMessage + "Invalid input"; //Line 28

JOptionPane.showMessageDialog(null, outputMessage, "Telephone Digit",
JOptionPane.PLAIN_MESSAGE); //Line 29

inputMessage = "Enter another uppercase letter "
+ "to find its corresponding "
+ "telephone digit.\n"
+ "To stop the program enter #.\n"
+ "Enter a letter:"; //Line 30

inputString = JOptionPane.showInputDialog(inputMessage); //Line 31
letter = inputString.charAt(0); //Line 32
}//end while
System.exit(0); //Line 33
}
}

/*
Sample Output:

*/