Regex pattern for numbers with dots

Question

I need a regex expression for this

any number then . and again number and .

So this is valid

1.3.164.1.2583.15.46
546.598.856.1.68.268.695.5         


        

Answer 1

You could match with the following regular expression.

(?<![.\d])\d+(?:\.\d+)+(?![.\d])

Start your engine!

The negative lookarounds are to avoid matching .1.3.164.1 and 1.3.164.1.. Including \d in the lookarounds is to avoid matching 1.3.16 in 1.3.164.1..

Java's regex engine performs the following operations.

(?<![.\d])  : negative lookbehind asserts following character is not
              preceded by a '.' or digit
\d+         : match 1+ digits
(?:\.\d+)   : match '.' then 1+ digits in a non-capture group
+           : match the non-capture group 1+ times
(?![.\d])   : negative lookahead asserts preceding character is not
              followed by a '.' or digit

Answer 2

I was thinking recursive regex here, and my pattern is:

pattern = "\\d+.\\d+(?:.\\d+.\\d+)*"

Answer 3

This one [0-9]+([.][0-9]+)* equivalent to \\d+([.]\\d+)* is valid for

1.3.164.1.2583.15.46 , 546.598.856.1.68.268.695.5955565 and 5465988561682686955955565

And this one [0-9]+([.][0-9]+)+ equivalent to \\d+([.]\\d+)+ is valid for

1.3.164.1.2583.15.46 and 546.598.856.1.68.268.695.5955565 but not for 5465988561682686955955565

Answer 4

Something like this should work:

(\\d+\\.?)+

Edit

Yep, not clear from the description if a final . is allowed (assuming an initial one is not).

If not:

(\\d+\\.?)*\\d+ or \\d+(\\.\\d+)* (if that seems more logical)

Test

for (String test : asList("1.3.164.1.2583.15.46",
    "546.598.856.1.68.268.695.5955565", "5..........", "...56.5656"))
    System.out.println(test.matches("\\d+(\\.\\d+)*"));

produces:

true
true
false
false