Why do I use char[] instead of string when I use password?

Security reasons are the biggest. String is a constant, which means that once it is created and memory dumps, there is no way to erase the data until the garbage collector clears it.

When it is an array, you can initialize it once and erase or change the data at any time. If you overwrite the data in the array, the password is nowhere to be found.

That's why we use char [] to prevent certain strikers.

To put it simply

    public static void main(String[] args) {
        Object pw = "Password";
        System.out.println("String: " + pw);

        pw = "Password".toCharArray();
        System.out.println("Array: " + pw);
    }

If you accidentally expose the password in these codes, the string is immediately output, but char[] is relatively safe.

    String: Password
    Array: [C@5829428e