Adding binary numbers

Question

Does anyone know how to add 2 binary numbers, entered as binary, in Java?

For example, 1010 + 10 = 1100.

Answer 1

The original solution by Martijn will not work for large binary numbers. The below code can be used to overcome that.

public String addBinary(String s1, String s2) {
    StringBuilder sb = new StringBuilder();
    int i = s1.length() - 1, j = s2.length() -1, carry = 0;
    while (i >= 0 || j >= 0) {
        int sum = carry;
        if (j >= 0) sum += s2.charAt(j--) - '0';
        if (i >= 0) sum += s1.charAt(i--) - '0';
        sb.append(sum % 2);
        carry = sum / 2;
    }
    if (carry != 0) sb.append(carry);
    return sb.reverse().toString();
}