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

Java solution

static String addBinary(String a, String b) {

    int lenA = a.length();
    int lenB = b.length();
    int i = 0;

    StringBuilder sb = new StringBuilder();
    int rem = Math.abs(lenA-lenB);
    while(rem >0){
        sb.append('0');
        rem--;
    }
    if(lenA > lenB){
        sb.append(b);  
        b = sb.toString();
    }else{
        sb.append(a);
        a = sb.toString();
    }

    sb = new StringBuilder();
    char carry = '0';
    i = a.length();
    while(i > 0){
        if(a.charAt(i-1) == b.charAt(i-1)){
            sb.append(carry);
            if(a.charAt(i-1) == '1'){
                carry = '1';
            }else{
                carry = '0';
            }
        }else{
            if(carry == '1'){
                sb.append('0');
                carry = '1';
            }else{
                carry = '0';
                sb.append('1');
            }
        }
        i--;
    }

    if(carry == '1'){
        sb.append(carry);
    }

    sb.reverse();
    return sb.toString();

}