正则表达式内部数字检查

Question

I have the following regex but it fails (the inner digits with the points) :

([0-9]{1,3}\.?[0-9]{1,3}\.?[0-9]{1,3})

I want that it covers the following cases:

• 123 valid
• 123.4 valid
• 123.44 valid
• 123.445 valid
• 123. 33 .3 not ok (regex validates it as true)
• 123. 3 .3 not ok (regex validates it as true)
• 123.333.3 valid
• 123.333.34 valid
• 123.333.344 valid

Can you please help me?

Answer 1

You have multiple case, I would like to use | the or operator like this :

^([0-9]{1,3}|[0-9]{1,3}\.[0-9]{1,3}|[0-9]{1,3}\.[0-9]{3}\.[0-9]{1,3})$
^           ^                      ^                                 ^

you can check the regex demo

---

details

The regex match three cases :

case 1

[0-9]{1,3}

this will match one or more digit

case 2

[0-9]{1,3}\.[0-9]{1,3}

this will match one or more digit followed by a dot then one or more digits

case 3

[0-9]{1,3}\.[0-9]{3}\.[0-9]{1,3}

this will match one or more digit followed by a dot then three digits then a dot then one or three digits

Note you can replace [0-9] with just \\d your regex can be :

^(\d{1,3}|\d{1,3}\.\d{1,3}|\d{1,3}\.\d{3}\.\d{1,3})$

Answer 2

How about this one (demo at Regex101 ). It's pretty short and straightforward Regex:

(^\d{3}\.\d{3}\.\d{1,3}$)|(^\d{3}\.\d{1,3}$)|(^\d{3}$)

This recognizes three valid separate groups.

• (^\\d{3}\\.\\d{3}\\.\\d{1,3}$) as a group which must have 3 digits, a dot, 3 more digits, a dot and 1-3 digits.
• (^\\d{3}\\.\\d{1,3}$) as a group which must have 3 digits, a dot and 1-3 digits.
• (^\\d{3}$) as a group which must have 1-3 digits.

These groups split with the or ( | ) statement.

However, since you have tagged java , why don't let Java to take some responsibility and help Regex where isn't strong? I would rather match the format ((?:\\d{1,3}\\.?)+) and check programmatically whether the count of numbers is valid.

Answer 3

Use the following expression with .matches :

s.matches("\\d{1,3}(?:\\.\\d{3})?(?:\\.\\d{1,3})?")

See the regex demo

Details

• ^ - implicit, not necessary as the pattern is used in .matches that requires a full string match
• \\d{1,3} - 1 to 3 digits
• (?:\\.\\d{3})? - an optional . and 3 digits
• (?:\\.\\d{1,3})? - an optional sequence of . and 1 to 3 digits
• $ - implicit, not necessary since the pattern is used in .matches that requires a full string match