Regular Expression for floating point numeric field

Question

Hi,
the requirements for the field are as follows:
- floating point numeric field 7 digits in length
- the field must contain a decimal (dot) and either one, two or three digits to the right of the decimal
- (leading zeroes are required if needed to fill up the 7 characters)
My example shown below does not check for the length of 7 characters:
public static void main(String[] args) {
    String str = "04100.0";
    System.out.println(str);
    Pattern f_1To7 = Pattern.compile("^([0-9]*\\.[0-9]{1,3})$");
    Matcher matcher = f_1To7.matcher(str);
    if (matcher.find()) {
        // yes, we've found something
        System.out.println("We matched the pattern!");
    } else {
        System.out.println("Better luck next time!");
}When changing the pattern to
^([0-9]*\\.[0-9]{1,3}){7}$the whole expression will be repeated 7 times - but I would like to have to whole String to be 7 characters long.
Here are some examples for the field:
050.500 or 04100.0Thanks a lot and best regards,
- Stephan

Answer 1

Jackler wrote:
Perhaps I did not express clearly enough. My problem is not a java issue - what I need is a regular expression (pattern) suiting my requirements:
-floating point numeric field 7 digits in length
-contains a decimal and either one, two or three digits to the right of the decimal
...Assuming that you are going to use Java*, you could use a lookahead at the start of your regex:
"^(?=\\d{4,6}\\.\\d{1,3}$).{8}$"Meaning:
^             # match the start of the string
(?=           #
  \d{4,6}     #   ensure that there are between 4 and 6 digits...
  \.          #   followed by a DOT...
  \d{1,3}     #   followed by 1 to 3 digits
.{8}$         # match exactly 8 characters directly followed by the end of the string* or some other language that has look-ahead support (most PCRE implementations have them)