Parse double with specific decimal symbol

Question

How can I set a specific decimal separator for a double? The next method should parse the string version of a double only if the separator is the given value, but works for both, DOT or COMMA. I want it to return true only if the string has the given separator.

public static boolean isValid(char decimalSeparator) {
    DecimalFormat df = new DecimalFormat();
    DecimalFormatSymbols symbols = new DecimalFormatSymbols();
    symbols.setDecimalSeparator(decimalSeparator);
    df.setDecimalFormatSymbols(symbols);

    try {
        df.parse("22,22").doubleValue();
        return true;
    } catch (ParseException e) {
        return false;
    }
}

Answer 1

Here is the problem. The javadoc for parse(String) says

"Parses text from the beginning of the given string to produce a number. The method may not use the entire text of the given string. "

When you provide a string with the "wrong" decimal separator, this parse method will stop when it gets to this character, and (probably) return a Long value rather than a Double value. A ParseException is only thrown if the first unexpected character is the first character of the string.

The solution is to use the two argument parse method ( javadoc ):

    ParsePosition pp = new ParsePosition(0);
    String str = "22,22";
    df.parse(str, pp);
    return pp.getIndex() == str.length() && pp.getErrorIndex() == -1;

Note that this overload of parse does not throw ParseException

Answer 2

Does this help you?

public static void main(String[] args) {

    isValid("22,22", ",");
    isValid("22.22", ".");
    isValid("2222", ",");
    isValid("2222", ".");
    isValid(",22", ",");
    isValid("22,", ",");
    isValid("22,22", ".");



}

static boolean isValid(String number, String ds) {
    ds = ds.replace(".", "\\.");
    String[] parts = number.split(ds);

    try {
        switch (parts.length) {
            case 0: Integer.parseInt(number); break;
            case 1: Integer.parseInt(parts[0]); break;
            case 2: Integer.parseInt(parts[0]); Integer.parseInt(parts[1]); break;
            default: throw new NumberFormatException();
        }
        return true;
    } catch(NumberFormatException e) {
        return false;
    } 


}

you may add extra conditions, like check the decimal-separator's length if it has only one char, or if ",22" can be "0,22"