add binary

Given two binary strings, return their sum (also a binary string).

For example,
a = "11"
b = "1"
Return "100".

public String addBinary(String a, String b) {if (a == null || a.isEmpty())return b;if (b == null || b.isEmpty())return a;StringBuilder stb = new StringBuilder();int i = a.length() - 1;int j = b.length() - 1;int aBit;int bBit;int carry = 0;int result;while (i >= 0 || j >= 0 || carry == 1) {aBit = (i >= 0) ? Character.getNumericValue(a.charAt(i--)) : 0;bBit = (j >= 0) ? Character.getNumericValue(b.charAt(j--)) : 0;result = aBit ^ bBit ^ carry;carry = ((aBit + bBit + carry) >= 2) ? 1 : 0;stb.append(result);}return stb.reverse().toString();}