MATHEMATICAL FUNCTIONS, CHARACTERS, AND STRINGS - Introduction to Java Programming: Comprehensive Version - page 143

L ISTING 4.4

HexDigit2Dec.java
1 import java.util.Scanner;
2
3 public class HexDigit2Dec {
4 public static void main(String[] args) {
5 Scanner input = new Scanner(System.in);
6 System.out.print( "Enter a hex digit: " );
7 String hexString = input.nextLine();
8
9 // Check if the hex string has exactly one character
10 if (hexString.length() != 1 ) {
11 System.out.println( "You must enter exactly one character" );
12 System.exit( 1 );
13 }
14
15 // Display decimal value for the hex digit
16 char ch = hexString.charAt( 0 );
17 if (ch <= 'F' && ch >= 'A' ) {
18 int value = ch - 'A' + 10 ;
19 System.out.println( "The decimal value for hex digit "
20 + ch + " is " + value);
21 }
22 else if (Character.isDigit(ch)) {
23 System.out.println( "The decimal value for hex digit "
24 + ch + " is " + ch);
25 }
26 else {
27 System.out.println(ch + " is an invalid input" );
28 }
29 }
30 }

VideoNote
Convert hex to decimal

input string

check length

is A-F?

is 0-9?

Enter a hex digit: AB7C
You must enter exactly one character

Enter a hex digit: B
The decimal value for hex digit B is 11

Enter a hex digit: 8
The decimal value for hex digit 8 is 8

Enter a hex digit: T
T is an invalid input

The program reads a string from the console (line 7) and checks if the string contains a
single character (line 10). If not, report an error and exit the program (line 12).
The program invokes the Character.toUpperCase method to obtain the character ch as
an uppercase letter (line 16). If ch is between 'A' and 'F' (line 17), the corresponding deci-
mal value is ch - 'A' + 10 (line 18). Note that ch - 'A' is 0 if ch is 'A' , ch - 'A' is 1