Regex for validating correct input for calculator

Question

I need to have some Calculator done, currently i'm dealing with the issue that I need to have only numbers (0,1,2,3,4,5,6,7,8,9) and operators (+, -, *, /, .) in my JTextField which is the user's input.

Currently my regex is like: String REGEX = "^[0-9]+[.]?[0-9]{0,1}$"; and it's from an example that I found over the web.

How do I have also to possibility to allow these operators: +, -, *, /? (the dot is already done)

The total idea is to have it like the Windows Calculator.
I'm not that strong in this topic, please advice.

EDIT: it also needs to have round braces like ( and )

what do you mean by "How do I having also to possibility to have the operators (+, -, *, /) ?" — Kick Buttowski, Jan 28 '15 at 17:21
They are like String, so I also need them to be printed in my `JTextField` — roeygol, Jan 28 '15 at 17:22
Are you validating the format of the input or if the input can be evaluated? — Luiggi Mendoza, Jan 28 '15 at 17:24
It's being typed by the user, so he can only type 0-9 and +-*/. It's need to be the same like Windows Calculator . — roeygol, Jan 28 '15 at 17:26
why do you only admit zero or one decimal? `[0-9]{0,1}`. It's a must? — Albert, Jan 28 '15 at 17:33
this is just an example from something over the we, feel free to do what you like — roeygol, Jan 28 '15 at 17:39

score 4 · Accepted Answer · answered Jan 28 '15 at 17:54

4

Here's an example that matches your requirements:

^[\d\+\/\*\.\- \(\)]*$

As a JAVA String this would be:

String regex = "^[\\d\\+\\/\\*\\.\\- \\(\\)]*$";

Note that I also added a SPACE to this list of allowed chars.

answered Jan 28 '15 at 17:54

jHilscher

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Can you please have also the numbers inside it ? – roeygol Jan 28 '15 at 17:59
I guess, this also validates non-sense expressions like `12.23/`, or `*()`. Maybe is ok to @RoeyGolzarpoor – Albert Jan 28 '15 at 18:00
\d is a representation for all numbers. Since chars like '+' also have a meaning in regex, you need to escape them. Java then needs to escape '\' as well. – jHilscher Jan 28 '15 at 18:00
@Albert This is true. But dealing with all the possible input constellations would be over the top for a regex. This regex more or less deals only with the set of chars you put into that field. – jHilscher Jan 28 '15 at 18:03
@jHilscher. Yeah! You are right. I've been trying, but I didn't succeed ;) – Albert Jan 28 '15 at 18:04
Agree with jHilscher, if you want to go further write a function that validates the input. Interesting ideas are found [here](http://stackoverflow.com/questions/3422673/evaluating-a-math-expression-given-in-string-form). – Josue Montano Jan 28 '15 at 18:06
Most of these escapes are superfluous, `^[\\d+*/.()-]+$` is enough and much more readable. – Toto Jan 28 '15 at 18:26

streetturtle · Answer 2 · 2015-01-28T21:34:19.657

2

Just in case somebody will need a bit more proper solution:

^(\d+[\+\-\*\/]{1})+\d+$

It is better because these strings won't pass:

45++6*6
12+4+
+2-6

You can test it here: https://regex101.com/r/zB7vV3/2

edited Jan 28 '15 at 21:34

answered Jan 28 '15 at 19:27

streetturtle

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'+2-6' could be a valid expression. And '-2-2' won't pass ether. – jHilscher Jan 29 '15 at 06:03

score 0 · Answer 3 · answered Jul 22 '16 at 09:43

0

my regex

^[\d\(]+[\d\+\-\*\/\(\)]+[\d\)]+$

passed:

3+3*5*(2+1)

not good yet:

1+2)
1+)

answered Jul 22 '16 at 09:43

Miao1007

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Regex for validating correct input for calculator

3 Answers3