How to check if a String is numeric in Java

Question

How would you check if a String was a number before parsing it?

Answer 1

public static boolean isNumeric(String str)
{
    return str.matches("-?\\d+(.\\d+)?");
}

CraigTP's regular expression (shown above) produces some false positives. E.g. "23y4" will be counted as a number because '.' matches any character not the decimal point.

Also it will reject any number with a leading '+'

An alternative which avoids these two minor problems is

public static boolean isNumeric(String str)
{
    return str.matches("[+-]?\\d*(\\.\\d+)?");
}