프로그래머스-신규 아이디 추천

class Solution {
    public String solution(String new_id) {
        String answer = new_id;
        
        
         new_id = new_id.toLowerCase(); //1단계
        new_id = new_id.replaceAll("[^0-9a-z-_.]", ""); //2단계
        new_id = new_id.replaceAll("\\.{2,}", "."); //3단계
        new_id = new_id.replaceAll("^\\.|\\.$", ""); //4단계
        new_id = new_id.length() == 0 ? "a" : new_id; //5단계
        new_id = new_id.length() >= 16 ? new_id.substring(0, 15).replaceAll("\\.$", "") : new_id; //6단계
        while (new_id.length() <= 2) {
            new_id += new_id.substring(new_id.length() - 1);
        }
             answer=new_id;
        return answer;
    }
}