Java – how to verify a secure password Regular expression on char []?

This question is a follow-up to this question:

Why is char[] preferred over String for passwords?

This is a good question to understand why char [] is used instead of string; However, it does not explain how to perform password verification on char [] in a secure manner That's what I want to know

In short, I need to check that my password meets the following requirements:

>At least one uppercase letter > at least one lowercase letter > at least one digit > at least one symbol > at least n characters but no more than m

Now I understand how to use regular expressions to perform validation... These answers show how to do this:

> Regexp Java for password validation > Password must be 8 characters including 1 uppercase letter,1 special character,alphanumeric characters

As far as I know, regular expression checking involves using strings It seems unsafe to use them because strings are immutable, so you can't clear them immediately after using them On the other hand, char [] can be cleared

So, how do I validate the password stored in char [] instead of a string?

I can traverse every character, but I have to create every set I want to test Ideally, it would be useful to be able to use regular expressions

In Java, I can check regular expressions in the following ways

String.matches(String regex)

or

Pattern pattern = Pattern.compile(String regex);
pattern.matcher(CharSequence testString).matches();

As you can see, neither of these methods supports the direct use of char []

Solution

I'll try to avoid complex regular expressions, and I'll suggest something like –

boolean validatePassword(char[] password,int n,int m) {
  if (password == null || password.length < n || password.length > m) {
    return false;
  }
  boolean upper = false;
  boolean lower = false;
  boolean digit = false;
  boolean symbol = false;
  for (char ch : password) {
    if (Character.isUpperCase(ch)) {
      upper = true;
    } else if (Character.isLowerCase(ch)) {
      lower = true;
    } else if (Character.isDigit(ch)) {
      digit = true;
    } else { // or some symbol test.
      symbol = true;
    }
    // This short-circuits the rest of the loop when all criteria are true.
    if (upper && lower && digit && symbol) {
      return true;
    }
  }
  return upper && lower && digit && symbol;
}