java和javascript中的正则表达式\\ b

Question

Is there any difference of use regular expression \\b in java and js?
I tried below test:
in javascript:

console.log(/\w+\b/.test("test中文"));//true  

in java:

String regEx = "\\w+\\b";
text = "test中文";
Pattern pattern = Pattern.compile(regEx);
Matcher matcher = pattern.matcher(text);
while(matcher.find()) {
    System.out.println("matched");//never executed
}

Why the result of the two example above are not same?

Answer 1

That is because by default Java supports Unicode for \\b but not for \\w , while JavaScript doesn't support Unicode for both.

So \\w can only match [a-zA-Z0-9_] characters (in our case test ) but \\b can't accept place (marked with | )

test|中文

as between alphabetic and non-alphabetic Unicode standards because both t and 中 are considered alphabetic characters by Unicode.

If you want to have \\b which will ignore Unicode you can use look-around mechanism and rewrite it as (?:(?<=\\\\w)(?!\\\\w)|(?<!\\\\w)(?=\\\\w)) , or in case of this example simple (?!\\\\w) instead of \\\\b will also work.

If you want \\w to also support Unicode compile your pattern with Pattern.UNICODE_CHARACTER_CLASS flag (which can also be written as flag expression (?U) )

Answer 2

The Jeva regex looks for a sequence of word characters, ie [a-zA-Z_0-9]+ preceding a word boundary. But 中文 doesn't fit \\w . If you use \\\\b alone, you'll find two matches: begin and end of the string.

As has been pointed out by georg, Javascript isn't interpreting characters the same way as Java's Regex engine.