Creating Regular Expression with Variable in Java

Question

I am a bit new to Regular Expressions. I am trying to create a Regular Expression in Java with a variable inside.

I would like to match "var", "(var)", "[var]", or "{var}" and any case variation of the variable var.

I have tried this, and it seems to have an exception:
java.util.regex.PatternSyntaxException: Unclosed character class near index 20

Does anyone have any suggestions how to fix and improve this?

String s = "[Tom] The rest of the title";
String v = "Tom";

s = s.replaceAll("(?i)[({/[]*" + v + "[)}\]]*", "");
System.out.println(s);

Should [Tom) match in your example?

Andrew Rueckert
– Andrew Rueckert

2016-06-16 00:36:25 +00:00
Commented Jun 16, 2016 at 0:36 — Andrew Rueckert
– Andrew Rueckert, Commented Jun 16, 2016 at 0:36
@AndrewRueckert Thanks for the response, no it should not.

Ninja
– Ninja

2016-06-16 00:38:45 +00:00
Commented Jun 16, 2016 at 0:38 — Ninja
– Ninja, Commented Jun 16, 2016 at 0:38

krokodilko · Accepted Answer · 2016-06-16 01:02:20Z

1

Try:

String s = "[Tom] The rest of the title";
String v = "Tom";

String myRegexp = String.format("(?i)\\[%s\\]|\\{%s\\}|\\(%s\\)|%s", v,v,v,v);
System.out.println(myRegexp);

s = s.replaceAll(myRegexp, "");
System.out.println(s);

This line:

String myRegexp = String.format("(?i)\\[%s\\]|\\{%s\\}|\\(%s\\)|%s", v,v,v,v);

builds a simple regular expression: (?i)\[Tom\]|\{Tom\}|\(Tom\)|Tom

All braces: {}[]() are special characters in regular expressions, and they have to be escaped by \ character (in Java string it must be \\).

answered Jun 16, 2016 at 1:02

krokodilko

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4 Comments

Ninja Over a year ago

Thanks for your response! Does this work for "too cool for school" to "[Too Cool for School] Hello"? It doesn't seem to remove this from the title!

krokodilko Over a year ago

Yes it works if you replace Tom with a new string and assign it to v ==> String v = "Too Cool for School";

Ninja Over a year ago

great answer! This is exactly what I was looking for, but extending it a bit more, what about removing all special characters around "Tom"? For example, the string could be something like "{[[Tom]]}" and I would want to replace the entire string with an empty string! Is it possible to remove all characters until an empty space on both sides?

Ninja Over a year ago

How would you match any number of special characters on both sides?

Andrew Rueckert · Accepted Answer · 2016-06-16 01:00:25Z

1

Matching pairs of braces ( to ), { to }, etc. is going to be messy with regular expressions, since the relationship isn't built into the language. A naieve solution would be:

String s = "[Tom] The rest of the title (TOM] tom";
String v = "Tom";
Pattern p = Pattern.compile("\\(" + v + "\\)|\\{" + v + "\\}|\\[" + v + "\\]|(?![{(\\[])" + v + "(?![})\\]])", Pattern.CASE_INSENSITIVE);
Matcher m = p.matcher(s);
System.out.println('\'' + m.replaceAll("") + '\'');
// ' The rest of the title (TOM] '

The head-ache-y part of regular expressions in Java is that you need to double escape any literal characters with \\, since you want a literal backslash character to appear in the string that you're passing to the regex compiler.

answered Jun 16, 2016 at 1:00

Andrew Rueckert

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1 Comment

Ninja Over a year ago

Is there anything that's more readable / elegant that works for most of the cases?

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