Decimal to octal conversion using Java

Decimal to octal conversion using java :

In this article we will discuss decimal to octal conversion using java. For this purpose we need to ask a decimal number from user and convert that decimal number to its octal equivalent form and then print the converted number on to the screen.
For conversion, we divide the decimal number by 8 and get the quotient for the next iteration and continuously store the remainder value in an array in reverse order till the decimal number is greater than 0. For better understanding with an example just have a look towards the diagram shown at the right.
decimal to octal conversion

Working :

  • Take the decimal number from the user and store it in variable say decimal.
  • Create an array say octal to store the octal representation of the given decimal number.
  • Run a loop until decimal is not equal to 0 i.e, (decimal !=0)
  • Inside the loop insert the remainder that achieved by dividing decimal from 8 i.e, (decimal%8)
  • Coming out from the loop print the octal array in reverse order.

Code for Decimal to Octal conversion using java:

//Java program to convert decimal number to octal number
import java.util.Scanner;
public class Decimal_To_Octal
public static void main(String args[])
//scanner class object creation
Scanner sc = new Scanner(;
//input from user
System.out.print("Enter a Decimal number : ");
int decimal = sc.nextInt();
//integer array for storing octal digits
int octal[] = new int[20];
int i = 0;
//writing logic for the conversion
while(decimal > 0)
int r = decimal % 8;
octal[i++] = r;
decimal = decimal/8;
//printing result
System.out.print("Octal number : ");
for(int j = i-1 ; j >= 0 ; j--)
//closing scanner class(not compulsory, but good practice)

Output :

Enter a Decimal number : 147
Octal number : 223

Optimize Algorithm

  • Initialize ocatalNum to 0 and countVal to 1 and the decimal number as n
  • Find the remainder when decimal number divided by 8
  • Update octal number by octalNum + (remainder * countval)
  • Increase countval by countval*10
  • Divide decimal number by 8
  • Repeat from the second step until the decimal number is zero
// JAVA program to convert decimal

class GFG {

    // function to calculate the octal value of the given

    // decimal number

    static void octaltodecimal(int deciNum)


        int octalNum = 0, countval = 1;

        int dNo = deciNum;

        while (deciNum != 0) {

            // decimals remainder is calculated

            int remainder = deciNum % 8;

            // storing the octalvalue

            octalNum += remainder * countval;

            // storing exponential value

            countval = countval * 10;

            deciNum /= 8;




    // Driver Code

    public static void main(String[] args)


        int n = 33;

        // Function Call