Java Program to Add Two Binary Strings

Last Updated : 19 May, 2023

When two binary strings are added, then the sum returned is also a binary string.

Example:

Input : x = "10", y = "01" Output: "11"

Input : x = "110", y = "011" Output: "1001" Explanation: 110 + 011 =1001

Approach 1:

Here, we need to start adding from the right side and when the sum returned is more than one then store the carry for the next digits.

Let us see a program in order to get a clear concept of the above topic.

Example:

Java

// Java program to add two binary strings public class GFG {  // Function to add two binary strings  static String add_Binary(String x, String y)  {  int num1 = Integer.parseInt(x, 2);  // converting binary string into integer(decimal  // number)  int num2 = Integer.parseInt(y, 2);  // converting binary string into integer(decimal  // number)  int sum = num1 + num2;  // Adding those two decimal numbers and storing in  // sum  String result = Integer.toBinaryString(sum);  // Converting that resultant decimal into binary  // string  return result;  }  // Main driver method  public static void main(String args[])  {  String x = "011011", y = "1010111";  System.out.print(add_Binary(x, y));  } }

Output

Approach 2: Two Pointer

Initialize two pointers at the end of both strings, let's call them i and j.
Initialize a variable carry to 0.
While i and j are greater than or equal to 0, do the following:
- Convert the current digits at i and j to integers (0 if the pointer is out of bounds).
- Add the integers together with the carry value.
- If the sum is 0 or 1, add it to the result string and set carry to 0.
- If the sum is 2, add 0 to the result string and set carry to 1.
- If the sum is 3, add 1 to the result string and set carry to 1.
- Decrement i and j by 1.
If there is still a carry left over, add it to the front of the result string.
Reverse the result string and return it.

Java

import java.io.*; // Class class GFG {  // Method  public static String addBinary(String x, String y)  {  int i = x.length() - 1, j = y.length() - 1;  int carry = 0;  StringBuilder result = new StringBuilder();  while (i >= 0 || j >= 0) {  int sum = carry;  if (i >= 0) {  sum += x.charAt(i) - '0';  }  if (j >= 0) {  sum += y.charAt(j) - '0';  }  if (sum == 0 || sum == 1) {  result.append(sum);  carry = 0;  }  else if (sum == 2) {  result.append("0");  carry = 1;  }  else {  result.append("1");  carry = 1;  }  i--;  j--;  }  if (carry == 1) {  result.append("1");  }  return result.reverse().toString();  }  // Main driver method  public static void main(String[] args)  {  String x = "011011";  String y = "1010111";    System.out.println(addBinary(x, y));  } }