Thread: need to know if the object is a number or character

Can these numbers be decimal numbers? Or are they guaranteed to be integers? If they are integers, you can just use the Character.isDigit methods. Otherwise, it's easiest to use the Regex class and regular expressions. Also, you can use the Character.isLetter method to see if a certain character is a letter.

I'd recommend looking through the Sun Regex Tutorials, or any other tutorials dealing with regular expressions to understand how they work. Here's a regex I've used that picks up pretty much every form of numbers (integers, decimals, scientific notation or any power 10 expression)

Pattern.compile("([0-9]*[.]?[0-9]+[eE]{1}-?[0-9]+)"
                                              + "|([0-9]+[.]?[0-9]*[eE]{1}-?[0-9]+)" + "|([0-9]*[.]?[0-9]+)"
                                              + "|([0-9]+)");

Note: It only picks up non-negative numbers. It can easily be modified to pick up negative numbers, but the calculator I had handled minus signs universally, so there was no need to detect negative numbers.

To use Java's Regex package, you must first create a regex (like above) using the Patern.compile() factory constructor. This will give you a Pattern object which has a method that builds a Matcher object. This Matcher object is the one you'll use to detect the item in question:

Pattern myRegex = Pattern.compile("([0-9]*[.]?[0-9]+[eE]{1}-?[0-9]+)"
                                              + "|([0-9]+[.]?[0-9]*[eE]{1}-?[0-9]+)" + "|([0-9]*[.]?[0-9]+)"
                                              + "|([0-9]+)");
Matcher matchThis = myRegex.matcher("123.456e3");
if (matchThis.find())
{
     System.out.println("Found a number! It's string representation is this: " + matchThis.group());
}

Of course, once you have the pure form of the number, you can put that into the Double.parseDouble() method and get out the value you want.

But then you have to get Apache I prefer to start with just the standard Java API. Besides, learning regular expressions is a good idea anyways.