How to escape a character in Regex expression in Java

Question

I have a regex expression which removes all non alphanumeric characters. It is working fine for all special characters apart from ^. Below is the regex expression I am using.

String strRefernce = strReference.replaceAll("[^\\p{IsAlphabetic}^\\p{IsDigit}]", "").toUpperCase();

I tried modifying it to

String strRefernce = strReference.replaceAll("[^\\p{IsAlphabetic}^\\p{IsDigit}]\\^", "").toUpperCase();

and

String strRefernce = strReference.replaceAll("[^\\p{IsAlphabetic}^\\p{IsDigit}\\^]", "").toUpperCase();

But these are also not able to remove this symbol. Can someone please help me with this.

Answer 1

The first ^ inside [^...] is a negation mark making the character class a negated one (matching characters other than what is inside).

The second one inside is considered a literal - thus, it should not be matched with the regex. Remove it, and a caret will get matched with it:

"[^\\p{IsAlphabetic}\\p{IsDigit}]"

or even shorter:

"(?U)\\P{Alnum}"

The \\P{Alnum} class stands for any character other than an alphanumeric character: [\\p{Alpha}\\p{Digit}] (see Java regex reference ). When you pass (?U) , the \\P{Alnum} class will not match Unicode letters. See this IDEONE demo .

Add a + at the end if you want to remove whole chunks of symbols other than \\\\p{IsAlphabetic} and \\\\p{IsDigit} .

Answer 2

This works as well.

System.out.println("Text 尖酸[刻薄 ^, More _0As text °ÑÑ"".replaceAll("(?U)[^[\\W_]]+", " "));  

Output

Text 尖酸 刻薄 More 0As text Ñ Ñ 

Not sure but the word might be the more comprehensive list of alphanum characters.

[\\\\W_] is a class containing non-words and an underscore.

When put into a negative Java class construct it becomes

[^[\\\\W_]] is a negative class of a union between nothing and
a class containing non-words and an underscore.