(Phone keypads) The international standard letter/number mapping for telephones is shown in Programming Exercise 4.15. Write a method that returns a number, given an uppercase letter, as follows:

/*
(Phone keypads) The international standard letter/number mapping for telephones
is shown in Programming Exercise 4.15. Write a method that returns a number,
given an uppercase letter, as follows:
int getNumber(char uppercaseLetter)
Write a test program that prompts the user to enter a phone number as a string.
The input number may contain letters. The program translates a letter (uppercase
or lowercase) to a digit and leaves all other characters intact.
*/
import java.util.Scanner;

public class Exercise_06_21 {
	/** Main Method */
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in); // Create a Scanner

		// Prompt the user to enter a phone number as a string
		System.out.print("Enter a string: ");
		String string = input.nextLine();
		
		// Translate a letter to a digit and leaves all other character intact
		for (int i = 0; i < string.length(); i++) {
			if (Character.isLetter(string.charAt(i)))
				System.out.print(getNumber(Character.toUpperCase(string.charAt(i))));
			else
				System.out.print(string.charAt(i));
		}
		System.out.println();
	}
	
	/** Method getNumber returns a number, given an uppercase letter */
	public static int getNumber(char uppercaseLetter) {
		// Return the character's number reference in the international 
		// standard letter/number mapping for telephones
		if (uppercaseLetter >= 'W')
			return 9;
		else if (uppercaseLetter >= 'T')
			return 8;
		else if (uppercaseLetter >= 'P')
			return 7;
		else if (uppercaseLetter >= 'M')
			return 6;
		else if (uppercaseLetter >= 'J')
			return 5;
		else if (uppercaseLetter >= 'G')
			return 4;
		else if (uppercaseLetter >= 'D')
			return 3;
		else 
			return 2;
	}
}