Java: Convert a hexadecimal to a octal number

Last update on May 12 2025 13:17:49 (UTC/GMT +8 hours)

Hexadecimal to Octal Converter

Write a Java program to convert a hexadecimal value into an octal 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.

Octal number: The octal numeral system is the base-8 number system, and uses the digits 0 to 7.

Test Data:
Input any hexadecimal number: 40

Pictorial Presentation: Hexadecimal to Octal number

Sample Solution:

Java Code:

import java.util.Scanner;

public class Main {
    // Function to convert a hexadecimal string to a decimal integer
    public static int hex_to_oct(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, i = 1, j;
        int octal_num[] = new int[100];
        Scanner in = new Scanner(System.in);

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

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

        // Convert the decimal number to octal
        while (dec_num != 0) {
            octal_num[i++] = dec_num % 8;
            dec_num = dec_num / 8;
        }

        // Display the equivalent octal number
        System.out.print("Equivalent of octal number is: ");
        for (j = i - 1; j > 0; j--) {
            System.out.print(octal_num[j]);
        }

        System.out.print("\n");
    }

Explanation:

In the exercise above -

• First, it defines a method "hex_to_oct()" that takes a hexadecimal string 's' as input and converts it to its decimal equivalent. It initializes a string 'digits' containing the hexadecimal digits (0-9 and A-F), ensures that the input string 's' is in uppercase, and iterates through the characters to compute the decimal value.
• 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_oct ()" method, passing 'hexdec_num' as an argument, to convert the hexadecimal string to its decimal equivalent and stores it in the 'dec_num' variable.
• Then, it converts the decimal number to octal:
• It initializes an integer array 'octal_num' to store the octal digits.
• It enters a loop to perform the decimal-to-octal conversion:
• In each iteration, it calculates the remainder when 'dec_num' is divided by 8 (which gives the least significant octal digit).
• It stores this remainder in the 'octal_num' array.
• It updates 'dec_num' by dividing it by 8 to move to the next octal digit.
• It uses 'i' to keep track of each octal digit's position.
• Finally, it prints the octal representation of the original hexadecimal number by iterating through the 'octal_num' array in reverse order (from the most significant digit to the least significant digit).

Sample Output:

Input a hexadecimal number: 40                                                                                
Equivalent of octal number is: 100

Flowchart:

For more Practice: Solve these Related Problems:

• Convert a hexadecimal number longer than four digits to octal.
• Modify the program to allow the user to input multiple hexadecimal numbers for conversion.
• Write a program that performs hexadecimal-to-octal conversion without using decimal as an intermediate step.
• Implement hexadecimal-to-octal conversion using lookup tables.

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