Java: Convert a hexadecimal to a decimal number

Java Basic: Exercise-28 with Solution

Write a Java program to convert a hexadecimal value into a decimal number.

Hexadecimal number: This is a positional numeral system with a radix, or base, of 16. Hexadecimal uses sixteen distinct symbols, most often the symbols 0-9 to represent values zero to nine, and A, B, C, D, E, F (or alternatively a, b, c, d, e, f) to represent values ten to fifteen.

Decimal number: The decimal numeral system is the standard system for denoting integer and non-integer numbers. It is also called base-ten positional numeral system.

Test Data:
Input any hexadecimal number: 25

Pictorial Presentation: Hexadecimal to Decimal number

Sample Solution:

Java Code:

import java.util.Scanner;

public class Exercise28 {
    // Function to convert a hexadecimal string to a decimal integer
    public static int hex_to_decimal(String s) {
        // Define a string containing hexadecimal digits
        String digits = "0123456789ABCDEF";
        s = s.toUpperCase(); // Convert the input string to uppercase
        int val = 0; // Initialize the decimal value to 0

        // Iterate through each character in the input string
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i); // Get the current character
            int d = digits.indexOf(c); // Find the index of the character in the digits string
            val = 16 * val + d; // Update the decimal value using hexadecimal conversion
        }

        return val; // Return the decimal value
    }

    public static void main(String args[]) {
        String hexdec_num;
        int dec_num;
        Scanner scan = new Scanner(System.in);

        // Prompt the user to input a hexadecimal number
        System.out.print("Input a hexadecimal number: ");
        hexdec_num = scan.nextLine();

        // Call the hex_to_decimal function to convert the hexadecimal number to decimal
        dec_num = hex_to_decimal(hexdec_num);

        // Display the equivalent decimal number
        System.out.print("Equivalent decimal number is: " + dec_num + "\n");
    }
}

Explanation:

In the exercise above -

• First, it defines a method "hex_to_decimal()" that takes a hexadecimal string 's' as input and converts it to its decimal equivalent.
• The method initializes a string 'digits' containing the hexadecimal digits (0-9 and A-F) and ensures that the input string 's' is in uppercase to handle both uppercase and lowercase hexadecimal characters.
• It initializes an integer variable 'val' to store the decimal value.
• Next it iterates through each character 'c' in the input string 's' and finds the corresponding decimal value 'd' by looking up the index of 'c' in the 'digits' string.
• It updates the 'val' by multiplying it by 16 and adding the decimal value 'd'.
• The method returns the final decimal value 'val'.
• In the "main()" function, it takes a hexadecimal number as input from the user using the "Scanner" class and stores it in the 'hexdec_num' string.
• It calls the "hex_to_decimal()" method, passing 'hexdec_num' as an argument, to convert the hexadecimal string to its decimal equivalent and stores it in the 'dec_num' variable.
• Finally, it prints the decimal representation of the original hexadecimal number stored in the 'dec_num' variable.

Sample Output:

Input a hexadecimal number: 25                                                                                 
Equivalent decimal number is: 37

Flowchart:

Java Code Editor:

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