Java Program to Convert Decimal to Binary (Using Bitwise Operator, Array, Function, Recursion, and More)

Introduction

Converting a decimal number into its binary equivalent is a common task in programming, especially in low-level operations, competitive coding, and systems development.

In Java, this can be accomplished through a variety of techniques—from manual logic using loops to built-in methods.

This article explores different methods of decimal to binary conversion in Java with a focus on understanding the internal logic, bit manipulation, and recursive behavior.

Each method is explained step-by-step with a working program, sample output, and detailed code comments. These examples aim to help beginners and intermediate Java developers strengthen their understanding of number system conversions.

If you're searching for:

• java convert decimal to binary

• decimal to binary conversion java

• or a program to convert decimal to binary using recursion, array, or bitwise operations

Then this guide is exactly what you need.

 

Problem Statement

Objective:

Write a Java program that takes a decimal (base-10) number as input and converts it to its binary (base-2) representation.

 

Use Cases

Here are practical areas where converting decimal to binary is commonly used:

• Embedded Systems: Where binary values control hardware-level signals.

• Computer Networks: IP address calculations and subnetting often use binary.

• Bit Manipulation Tasks: Flags, masks, and bit-level programming require binary understanding.

• Data Compression & Encryption: Operate on binary sequences for performance and security.

• Academic & Competitive Programming: Often includes number system conversion challenges.

 

What You Will Learn

In this tutorial, you'll learn:

• How to convert decimal to binary using:

  • Manual logic (modulus and division)

  • Bitwise operators

  • Arrays and recursion

  • Java built-in methods

• How to use structured Java code with readable formatting

• Step-by-step logic explanation for each approach

• Sample output for better visualization

 

1. Java Program to Convert Decimal to Binary Using Bitwise Operator

// Java program to convert decimal to binary using bitwise operator
public class Main {
    public static void main(String[] args) {
        // Step-1 Declare and initialize the decimal number
        int num = 10;

        // Step-2 Check if the number is zero
        if (num == 0) {
            System.out.println("Binary representation: 0");
            return;
        }

        // Step-3 Store result using bitwise operations
        String binary = "";
        for (int i = 31; i >= 0; i--) {
            int bit = (num >> i) & 1;
            binary += bit;
        }

        // Step-4 Trim leading zeros
        binary = binary.replaceFirst("^0+(?!$)", "");

        // Step-5 Output result
        System.out.println("Binary representation: " + binary);
    }
}

Run

Output

 

Explanation of the Code:

• Declare Decimal Number: We initialize a decimal number num = 10.

• Check for Zero: If the number is zero, we print 0 directly.

• Use Bitwise Operation: A loop runs from 31 to 0, shifting the number right by i bits and extracting each bit using bitwise AND (& 1).

• Build Binary String: We build the binary string by appending bits from MSB to LSB.

• Remove Leading Zeros: Regex is used to strip leading zeros from the binary result.

• Output: Final binary string is printed.

 

2. Java Convert Decimal to Binary Using Integer Array

// Java program to convert decimal to binary using array
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Step-1 Declare variables
        Scanner sc = new Scanner(System.in);
        int[] binary = new int[32];
        int index = 0;

        // Step-2 Input decimal number
        System.out.print("Enter a decimal number: ");
        int num = sc.nextInt();

        // Step-3 Convert to binary using division
        while (num > 0) {
            binary[index++] = num % 2;
            num = num / 2;
        }

        // Step-4 Print binary in reverse order
        System.out.print("Binary representation: ");
        for (int i = index - 1; i >= 0; i--) {
            System.out.print(binary[i]);
        }

        System.out.println();
        sc.close();
    }
}

Run

Output

 

Explanation of the Code:

• Declare Array: A fixed-size array is used to store binary digits.

• Input Decimal Number: The user inputs a decimal number.

• Convert to Binary: Using division and modulo (% 2), we store the remainder in the array.

• Reverse Output: Since binary is built in reverse, we print from the last index to the first.

• Close Scanner: Free the resource after use.

 

3. Java Program to Convert Decimal to Binary Using Function

// Java program to convert decimal to binary using a function
import java.util.Scanner;

public class Main {

    // Function to convert decimal to binary and return result
    static String convertToBinary(int num) {
        String binary = "";
        while (num > 0) {
            binary = (num % 2) + binary;
            num = num / 2;
        }
        return binary.equals("") ? "0" : binary;
    }

    public static void main(String[] args) {
        // Step-1 Input
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a decimal number: ");
        int num = sc.nextInt();

        // Step-2 Convert using function
        String binary = convertToBinary(num);

        // Step-3 Output result
        System.out.println("Binary representation: " + binary);
        sc.close();
    }
}

Run

Output

 

Explanation of the Code:

• Create Function: convertToBinary(int num) is a utility function that handles the logic.

• Inside Function:

  • We use a while loop to build the binary string from LSB to MSB.

  • Each digit is prepended to the string.

• Main Method:

  • Takes input, calls the function, and prints the result.

 

4. Java Program to Convert Decimal to Binary Using Recursion

// Java program to convert decimal to binary using recursion
import java.util.Scanner;

public class Main {

    // Recursive function to print binary
    static void convertToBinary(int num) {
        if (num == 0)
            return;
        convertToBinary(num / 2);
        System.out.print(num % 2);
    }

    public static void main(String[] args) {
        // Step-1 Input
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a decimal number: ");
        int num = sc.nextInt();

        // Step-2 Handle zero case
        System.out.print("Binary representation: ");
        if (num == 0)
            System.out.print("0");
        else
            convertToBinary(num);

        System.out.println();
        sc.close();
    }
}

Run

Output

 

Explanation of the Code:

• Create Recursive Function: convertToBinary(int num) prints digits recursively.

• Recursive Logic:

  • It divides the number by 2 and calls itself until the base case (0).

  • After returning, it prints num % 2.

• Main Method:

  • Takes input and calls the function.

  • Handles zero as a special case.

 

5. Java Convert Decimal to Binary Using Built-in Method

// Java program using built-in Integer.toBinaryString()
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        // Step-1 Input
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a decimal number: ");
        int num = sc.nextInt();

        // Step-2 Use built-in method
        String binary = Integer.toBinaryString(num);

        // Step-3 Output result
        System.out.println("Binary representation: " + binary);
        sc.close();
    }
}

Run

Output

 

Explanation of the Code:

• Input: Read a decimal number using Scanner.

• Conversion: Integer.toBinaryString(num) converts the number directly.

• Output: Print the returned binary string.

 

Final Thoughts

Each of these methods provides a different perspective on how decimal to binary conversion in Java can be implemented. From bitwise logic to recursion and built-in utilities, every method helps build deeper knowledge about binary systems and Java programming fundamentals.