What can i doing here to detect the duplicate in the two methods

Two methods intValueOf and intValueOfOptional, which are very similar. I would like to modify the implementation so that the two methods use as little duplicated code.

Both methods contain a very complex condition. How can I simplify them, semantically related parts of the condition into variables with meaningful names?

Which refactorings from IntelliJ should I use for this?

public static int intValueOf(String str) {
    int idx = 0;
    int end;
    boolean sign = false;
    char ch;
    
    if ((str == null) || ((end = str.length()) == 0) || ((((ch = str.charAt(0)) < '0') || (ch > '9')) && (!(sign = ch == '-') || (++idx == end) || ((ch = str.charAt(idx)) < '0') || (ch > '9')))) {
        throw new NumberFormatException(str);
    }

    int ival = 0;
    for (; ; ival *= 10) {
        ival += '0' - ch;
        if (++idx == end) {
            return sign ? ival : -ival  ;
        }
        if (((ch = str.charAt(idx)) < '0') || (ch > '9')) {
            throw new NumberFormatException(str);
        }
    }
}




public static Optional<Integer> intValueOfOptional(String str) {
    int idx = 0;
    int end;
    boolean sign = false;
    char ch;

    if ((str == null) || ((end = str.length()) == 0) || ((((ch = str.charAt(0)) < '0') || (ch > '9')) && (!(sign = ch == '-') || (++idx == end) || ((ch = str.charAt(idx)) < '0') || (ch > '9')))) {
        return Optional.empty();
    }

    int ival = 0;
    for (; ; ival *= 10) {
        ival += '0' - ch;
        if (++idx == end) {
            return Optional.of(sign ? ival : -ival);
        }
        if (((ch = str.charAt(idx)) < '0') || (ch > '9')) {
            return Optional.empty();
        }
    }
}

}

You don't need any tools for that, just look at the distinctions in the code. It's the same logic although one throws when it's not a valid int where the other returns an empty Optional.

Just leverage one within the other e.g.

public static int intValueOf(String str) {
   return intValueOfOptional(str).orElseThrow(() -> new NumberFormatException(str));
}