regular expression which allows square brackets

Question

Below is my code which allows special characters, numbers, characters(upper and lower) .This program is working fine. My issue with square brackets.

public class MatchingSpecificCharacters {
    public static void main(String[] args) {

        String reg = "[A-Za-z0-9!$-~`?/@#%^*&()_+=<>.,';:|\" ]*";
        String line = "as[]d";

        System.out.println(line.matches(reg));


    }
}

output

true

In the program, I have used [] brackets to enclose all the characters, numbers , special characters . I have not used extra square brackets to allow as special charters but the program is allowing it. Can anyone tell me why it is allowing square brackets.Correct me If I am wrong.

score 5 · Accepted Answer · answered Aug 10 '15 at 13:47

5

You should escape the hyphen.

String reg = "[A-Za-z0-9!$\\-~`?/@#%^*&()_+=<>.,';:|\" ]*";
                           ^

or place it at the end

String reg = "[A-Za-z0-9!$~`?/@#%^*&()_+=<>.,';:|\" -]*";

This is what your regex matches (as instead of a hyphen, you defined a range from $ till ~):

answered Aug 10 '15 at 13:47

Wiktor Stribiżew

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The keyboard you have given, is not regular keyboard.Can give complete picture of the keyboard.(I don't know whether it is a keyboard). Please specify, it will be helpful to others also. – rajeev pani.. Sep 01 '15 at 06:50
1

It is not a keyboard, it is an [ASCII table](http://www.asciitable.com/) which is a part of the [Unicode code point table](http://unicode.org/charts/). Regex is using Unicode code point table to resolve character ranges in [character classes](http://www.regular-expressions.info/charclass.html). – Wiktor Stribiżew Sep 01 '15 at 06:54

score 1 · Answer 2 · edited May 23 '17 at 12:21

1

Since you are using a hyphen, you can either escape it or place it as the first or last character in the range:

[-a-z] or [a-z-]

Otherwise, [A-Za-z ... $-~ ... \" ] is trying to match all the given characters plus everything in between $ and ~, that you can visually see in stribizhev's good answer.

See also How to match hyphens with Regular Expression?:

[-] matches a hyphen.

[abc-] matches a, b, c or a hyphen.

[-abc] matches a, b, c or a hyphen.

[ab-d] matches a, b, c or d (only here the hyphen denotes a character range).

edited May 23 '17 at 12:21

Community

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answered Aug 10 '15 at 13:52

fedorqui

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Never escape hyphen as it is not special character. When it is used in a range put it at beginning or end to avoid matching the range format. – MaxZoom Aug 10 '15 at 18:36

regular expression which allows square brackets

output

2 Answers2