Java: Convert a hexadecimal to a decimal number

Last update on May 12 2025 13:17:50 (UTC/GMT +8 hours)

Hexadecimal to Decimal Converter

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

Java: Convert a hexadecimal to a 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:

Flowchart: Java exercises: Convert a hexadecimal to a decimal number

For more Practice: Solve these Related Problems:

Convert a hexadecimal number with lowercase letters to decimal.
Modify the program to allow the user to input multiple hexadecimal numbers for conversion.
Write a program to perform hexadecimal-to-decimal conversion without using built-in functions.
Implement hexadecimal-to-decimal conversion using recursion.

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