How to control CATCH errors in JAVA

Question

So i have these lines:

try {
   extra = Double.parseDouble(igu.txfExtra.getText());
} catch (NumberFormatException e1) {
   System.out.print("Error");               
}

It collects a double from a JTextField called txfExtra.

How can I say in the System.out.print if the error was made by introducing letters in the label for example? I mean, if the error was due to the "extra" collecting a String, show that the error was due to a string.

Also an extra question, how can i make "extra" to take values with BOTH "." and "," because due to localization it either takes for example "10.923" or either "10,923" i want it to accept both types of format when parsing the double.

Answer 1

In order to satisfy both requirements, you would need something else than Double.parseDouble(). For one, it will use the current locale; also, its error message won't be as detailed as you want to be.

A solution would be to go through a regex to parse the input string, and only if the regex passes, parse using a NumberFormat:

private static final Pattern NUMPATTERN = Pattern.compile("\\d+([.,])\\d+");

// ...

// Supposes a custom MyException class
public double doParseDouble(final String input)
    throws MyException
{
    final Matcher m = NUMPATTERN.matcher(input);
    if (!m.matches())
        throw new MyException("Non number characters in input");

    final String separator = m.group(1);
    final Locale locale = ".".equals(separator)
        ? Locale.US : Locale.FRENCH;

    final NumberFormat fmt = NumberFormat.getInstance(locale);

    try {
        return fmt.parse(input).doubleValue();
    } catch (NumberFormatException e) {
        throw new MyException(e);
    }
}

This is only sample code and lacks a LOT of features:

• restricts to only a subset of valid doubles (.1 will not be accepted for instance; or 1.4e-3);
• does not deal with overflows/underflows;
• others.