可以在DecimalFormat解析中指定小数位数的确切数目吗？

Question

I'm using DecimalFormat to parse strings representing decimal numbers. What I'd like to have is to a parsing function which checks the exact number of fractional digits in strings. In details, I want to check that the string has exactly two fractional digits (eg, "1.10" is valid, "1.1" is not valid).

Is it possible to have such behavior with DecimalFormat ? The instance built with following method doesn't work.

private static DecimalFormat decimalFormat() {
    final DecimalFormatSymbols decimalFormatSymbols = new DecimalFormatSymbols();
    decimalFormatSymbols.setDecimalSeparator('.');
    final DecimalFormat decimalFormat = new DecimalFormat("#0.00", decimalFormatSymbols);
    decimalFormat.setMinimumFractionDigits(2);
    decimalFormat.setParseBigDecimal(true);
    return decimalFormat;
}

Any suggestions?

Answer 1

Here is the documentation on setMinimumIntegerDigits : https://docs.oracle.com/javase/8/docs/api/java/text/DecimalFormat.html#setMinimumIntegerDigits-int-

newValue - the minimum number of integer digits to be shown; [...].

As far as I can understand, this does not act as a requirement, only as a format for the output.

Looking through the available functions for DecimalFormat , I can't see anything that would give you the number of fraction digits.

BUT, since you are using setParseBigDecimal(true) , parsing a string would then give you a BigDecimal which gives you access to the precision function : https://docs.oracle.com/javase/8/docs/api/java/math/BigDecimal.html#precision--

So what I suggest if you absolutely want to check the result of the parse (and not the string itself) for the correct number of digits is :

• set the minimum fraction digits to 0
• take the string
• parse it in BigDecimal
• use the BigDecima::precision function to check if the number of digits is correct.

Hope this helps.

Answer 2

It sounds like you're trying to validate a condition rather than convert a string to a given format. You can use regular expressions to do this. Here's an example method that I believe does what you want

public boolean hasTwoFractionalDigits(String text) {
    return Pattern.compile("^\\d+\\.\\d\\d$").matcher(text).find();
}

This will return true for "10.33" but false for "10.3". If this doesn't answer your question let me know.

Answer 3

if price has decimal(.) then decimal(.) always have digit as prefix and suffix both. ie ' 0.0 ' integer price is acceptable. max 2 fractional digit.

5, 5.0, 5.00 Accept 0, 0.0, 0.00 5. .5, 5.000, ., .0, .00, .000, 0. String = Error