Binary addition implementation

public static String add(String bits1, String bits2){
        bits1 = new StringBuilder(bits1).reverse().toString();
        bits2 = new StringBuilder(bits2).reverse().toString();

        StringBuilder result = new StringBuilder();

        char q = '0';//for cases like: (1+1+0)=0 and 1, this (1) is stored in 1
        for(int i = 0;i < bits1.length();i++){
            char bit1 = bits1.charAt(i);
            char bit2 = bits2.charAt(i);
            if(bit1 == '0'){
                if(bit2 == '0'){
                    if(q == '0'){//(0+0+0)=0 and 0
                        result.append('0');
                        q = '0';
                    }else if(q == '1'){//(0+0+1)=1 and 0
                        result.append('1');
                        q = '0';
                    }
                }else if(bit2 == '1'){
                    if(q == '0'){//(0+1+0)=1 and 0
                        result.append('1');
                        q = '0';
                    }else if(q == '1'){//(0+1+1)=0 and 1
                        result.append('0');
                        q = '1';
                    }
                }
            }else if(bit1 == '1'){
                if(bit2 == '0'){
                    if(q == '0'){//(1+0+0)=1 and 0
                        result.append('1');
                        q = '0';
                    }else if(q == '1'){//(1+0+1)=0 and 1
                        result.append('0');
                        q = '1';
                    }
                }else if(bit2 == '1'){
                    if(q == '0'){//(1+1+0)=0 and 1
                        result.append('0');
                        q = '1';
                    }else if(q == '1'){//(1+1+1)=1 and 1
                        result.append('1');
                        q = '1';
                    }
                }
            }
        }
        if(q == '1')//for cases like: bits1=111 bit2 == 001, which equals = 1000
            result.append('1');
        return result.reverse().toString();
    }