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javadecimalformatparseexception
marcel
marcel

Reputation: 407

DecimalFormat converts numbers with non-digits

Using DecimalFormat gives no parse exception when using this kind of number:

123hello

which is obviously not really a number, and converts to 123.0 value. How can I avoid this kind of behaviour?

As a side note hello123 does give an exception, which is correct.

Thanks, Marcel

Upvotes: 13

Views: 1977

Answers (3)

jtahlborn
jtahlborn

Reputation: 53694

Expanding on @Kal's answer, here's a utility method which you can use with any formatter to do "strict" parsing (uses apache commons StringUtils):

public static Object parseStrict(Format fmt, String value)
    throws ParseException
{
    ParsePosition pos = new ParsePosition(0);
    Object result = fmt.parseObject(value, pos);
    if(pos.getIndex() < value.length()) {
        // ignore trailing blanks
        String trailing = value.substring(pos.getIndex());
        if(!StringUtils.isBlank(trailing)) {
            throw new ParseException("Failed parsing '" + value + "' due to extra trailing character(s) '" +
                                     trailing + "'", pos.getIndex());
        }
    }
    return result;
}

Upvotes: 2

Martijn Courteaux
Martijn Courteaux

Reputation: 68847

You can verify it is numeric using a RegEx:

String input = "123hello";
double d = parseDouble(input); // Runtime Error

public double parseDouble(String input, DecimalFormat format) throws NumberFormatException
{
    if (input.equals("-") || input.equals("-."))
       throw NumberFormatException.forInputString(input);
    if (!input.matches("\\-?[0-9]*(\\.[0-9]*)?"))
       throw NumberFormatException.forInputString(input);

    // From here, we are sure it is numeric.
    return format.parse(intput, new ParsePosition(0));
}

Upvotes: 0

Kal
Kal

Reputation: 24910

To do exact parsing, you can use 

public Number parse(String text,
                ParsePosition pos)

Initialize pos to 0 and when its finished it will give you the index after the last character that was used.

You can then compare this against string length to make sure the parse was accurate.

http://download.oracle.com/javase/1.4.2/docs/api/java/text/DecimalFormat.html#parse%28java.lang.String,%20java.text.ParsePosition%29

Upvotes: 10

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