Learning new things from new languages is fascinating. Trying to apply this
knowledge in the language you know doesn’t always go so well though. What
happens if you give isNumber a really really long string? Stack overflow :-/
Recursion is not one of Java’s strengths.
If you want a really fast isNumber and you’re only looking for chars ‘0’ thru
‘9', have a look at ERXStringUtilities.luhnCheck. Treating your chars as ints
is the fastest way I’ve found to determine isNumber. It is orders of magnitude
faster than Character.isDigit.
On Nov 12, 2014, at 4:32 AM, Theodore Petrosky <tedp...@yahoo.com> wrote:
> I am trying like mad to learn more. So I have decided to put time into
> Recursive algorithms. I do not want to start a conversation whether or not
> one should or should not use recursion in this example. That is a
> conversation for another day. I don’t believe that using it here will impact
> the app at all.
>
> As an experiment I am trying to use one in my validation method. Would one of
> you great minds take a look at this. It works, but I feel I am jumping
> through too many hoops. This is my first attempt so have a little pity:
>
>
> public String validateHeight(String value) throws ValidationException {
> value = value.trim();
>
> if (!isNumber(value)) {
> throw new ValidationException("There can be only
> numbers in the Height field! (value was " + value +")");
> }
> return value;
> }
>
> private boolean isNumber(String stringToCheck) {
> if (stringToCheck.length() == 0) return true;
> if (!Character.isDigit(stringToCheck.charAt(0))) return false;
> return isNumber(stringToCheck.substring(1,
> stringToCheck.length()));
> }
>
>
> My desire is to get better at this and learning recursion is very important.
> Also, when I look at other people’s code, there are times that there are
> recursive calls and I struggle to understand them.
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