Hexadecimal to Decimal Conversion in Java

Hexadecimal to Decimal Conversion

Hexadecimal to Decimal conversion is the process of converting a hexadecimal number (base-16) into its equivalent decimal number (base-10). Each hexadecimal digit represents a power of 16.

For example, the hexadecimal number 1F is equal to decimal 31 because:

(1 × 16¹) + (F × 16⁰) = 16 + 15 = 31

We will explore three methods to convert a hexadecimal number to a decimal number using Java programming.

Method 1: Using Loop

We extract each digit of the hexadecimal number, multiply it by the corresponding power of 16, and sum the results.

import java.util.Scanner;

public class Main {
    public static int hexToDecimal(String hex) {
        int decimal = 0, base = 1;
        for (int i = hex.length() - 1; i >= 0; i--) {
            char digit = hex.charAt(i);
            int value = (digit >= '0' && digit <= '9') ? digit - '0' : digit - 'A' + 10;
            decimal += value * base;
            base *= 16;
        }
        return decimal;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a hexadecimal number: ");
        String hex = scanner.next().toUpperCase();
        System.out.println("Decimal equivalent: " + hexToDecimal(hex));
        scanner.close();
    }
}
            

Output:

Enter a hexadecimal number: 1F
Decimal equivalent: 31

Method 2: Using Built-in Function

We can use Java's Integer.parseInt() method to directly convert a hexadecimal number to a decimal number.

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a hexadecimal number: ");
        String hex = scanner.next().toUpperCase();
        
        int decimal = Integer.parseInt(hex, 16);
        System.out.println("Decimal equivalent: " + decimal);
        scanner.close();
    }
}
            

Output:

Enter a hexadecimal number: 1F
Decimal equivalent: 31

Method 3: Using Recursion

We recursively extract each digit and multiply it by the corresponding power of 16.

import java.util.Scanner;

public class Main {
    public static int hexToDecimalRecursive(String hex, int length, int index) {
        if (index == length)
            return 0;
        char digit = hex.charAt(index);
        int value = (digit >= '0' && digit <= '9') ? digit - '0' : digit - 'A' + 10;
        return value * (int) Math.pow(16, length - index - 1) + hexToDecimalRecursive(hex, length, index + 1);
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a hexadecimal number: ");
        String hex = scanner.next().toUpperCase();
        
        System.out.println("Decimal equivalent: " + hexToDecimalRecursive(hex, hex.length(), 0));
        scanner.close();
    }
}
            

Output:

Enter a hexadecimal number: 1F
Decimal equivalent: 31