Why does this Java regex cause "illegal escape character" errors?

Question

I'm working on a solution to a previous question, as best as I can, using regular expressions. My pattern is

"d{4}w{3}(0[1-9]|[12][0-9]|3[01])([01][0-9]|2[0-3])([0-5][0-9]){2}"

According to NetBeans, I have two illegal escape characters. I'm guessing it has to do with the d and w, but those are both valid in Java. Perhaps my syntax for a Java regular expression is off...

The entire line of code that is involved is:

userTimestampField = new FormattedTextField(
  new RegexFormatter(
    "d{4}w{3}(0[1-9]|[12][0-9]|3[01])([01][0-9]|2[0-3])([0-5][0-9]){2}"
));

question from:https://stackoverflow.com/questions/1379191/why-does-this-java-regex-cause-illegal-escape-character-errors

Answer 1

Assuming this regex is inside a Java String literal, you need to escape the backslashes for your d and w tags:

"\d{4}\w{3}(0[1-9]|[12][0-9]|3[01])([01][0-9]|2[0-3])([0-5][0-9]){2}"

This gets more, well, bonkers frankly, when you want to match backslashes:

public static void main(String[] args) {        
    Pattern p = Pattern.compile("\\\\"); //ERM, YEP: 8 OF THEM
    String s = "\\";
    Matcher m = p.matcher(s);
    System.out.println(s);
    System.out.println(m.matches());
}

\ //JUST TO MATCH TWO SLASHES :(
true