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 idea is same as discussed in few of the answers, but this one is a much shorter and easier to understand solution (steps are commented).

// Handles numbers which are way bigger.
public String addBinary(String a, String b) {
    StringBuilder sb = new StringBuilder();
    int i = a.length() - 1; 
    int j = b.length() -1;
    int carry = 0;
    while (i >= 0 || j >= 0) {
        int sum = carry;
        if (j >= 0) { sum += b.charAt(j--) - '0' };
        if (i >= 0) { sum += a.charAt(i--) - '0' };

        // Added number can be only 0 or 1
        sb.append(sum % 2);

        // Get the carry.
        carry = sum / 2;
    }

    if (carry != 0) { sb.append(carry); }

    // First reverse and then return.
    return sb.reverse().toString();
}