Best implementation for an isNumber(string) method

Question

In my limited experience, I\'ve been on several projects that have had some sort of string utility class with methods to determine if a given string is a number. The idea h

Answer 1

I think It could be faster than previous solutions if you do the following (Java):

public final static boolean isInteger(String in)
{
    char c;
    int length = in.length();
    boolean ret = length > 0;
    int i = ret && in.charAt(0) == '-' ? 1 : 0;
    for (; ret && i < length; i++)
    {
        c = in.charAt(i);
        ret = (c >= '0' && c <= '9');
    }
    return ret;
}

I ran the same code that Asaph ran and the result was:

This operation took 28 ms.

A huge difference (against 1691 ms and 2049 ms -on my computer). Take in account that this method does not validate if the string is null, so you should do that previously (including the String trimming)