Java program to convert decimal number to binary

Let’s learn java program to convert decimal number to binary.

Java program to convert decimal number to binary

How to convert a decimal number to binary is one of the frequently asked in interview.

I’m going to show you to convert decimal number to binary number without using predefined method.

So given number is 20 divide that by 2 to get quotient 10 and remainder 0.

Now at this point we get one binary digit, that is 0 as the remainder.

java program to convert decimal number to binary

Remember the remainder is what gives you the binary digit.

Now take quotient 10 again divide that by 2 and you get the quotient as 5 and remainder as 0.

Again take quotient 5. Divide that by 2 you will get the quotient as 2 and remainder as 1.

Repeat the same procedure divide that by 2, you will get quotient as 1 and remainder as 0.

Now in the last step quotient is 1 and remainder is 1. Now, collecting all the remainders, you get 00101. Actually this is not the binary number.

We have to read reverse, that is, 10100 (we have to read it from right to left).

In the below java program we have written function to convert decimal to binary in java.

In the below function first we store binary number in an integer array. Then set counter for binary array in while loop.

In while loop store remainder in binary array. Lastly print binary in reverse order.

Here’s the program to convert decimal number to binary.

import java.util.*;
public class DecimalToBinaryDemo
   // this function converts decimal to binary
   static void toBinary(int num)
      // here we are storing binary number
      int binaryNumber[] = new int[1000];
      // "count" variable is counter for binary array
      int count = 0;
      while(num > 0)
         // storing remainder in binary array
         binaryNumber[count] = num % 2;
         num = num / 2;
      // here we are printing binary in reverse order
      for(int a = count - 1; a >= 0; a--)
   public static void main(String[] args)
      int number = 20;



Also read – classes and objects in java