What does this Regex mean in Java? "(\\d+(\\.\\d+)?)"

Question

The code is:

Pattern p = Pattern.compile("(\\d+(\\.\\d+)?)");

just replace \\ with \ (because java needs escaping in Strings) and you have a regex, then you can check yourself what that means — Lino, Nov 06 '17 at 11:54
Visit this page : https://regex101.com, and check your Regex — Bikramjit Rajbongshi, Nov 06 '17 at 11:57
It will match a whole number, optionally followed by a decimal point and decimal component. — Tim Biegeleisen, Nov 06 '17 at 11:58
See the API documentation of class [`java.util.regex.Pattern`](https://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html). — Jesper, Nov 06 '17 at 12:05

score 2 · Answer 1 · answered Nov 06 '17 at 12:13

a. \d implies digit.
b. + sign implies one or more occurance of previous character.
c. \. -> since . is a special character in regex, we have to escape it with \.
d. Also, \ is a special escape character in java , hence from java perspective we need to add an additional \ to escape the backslash (\).

Thus, the pattern will reprent any number like: 0.01, 0.001, 1.0001, 100.00001 and so on. Basically any decimal number with a digit before and after the decimal point.

score 0 · Answer 2 · answered Nov 06 '17 at 12:04

The regex is a simplified version to recognize floating-point numbers: At least one digit optionally followed by a dot and at least a digit.

It's simplified because it only covers only number without a sign (i.e. only positive numbers, because you can't provide a - minus sign), it allows number presentations that are considered invalid, e.g. 000123.123 and lacks the support of numbers written in scientific syntax (e.g. 1.234e56).

What does this Regex mean in Java? "(\\d+(\\.\\d+)?)"

2 Answers2