Can you use zero-width matching regex in String split?

问题

System.out.println(
    Arrays.deepToString(
        "abc<def>ghi".split("(?:<)|(?:>)")
    )
);

This prints [abc, def, ghi], as if I had split on "<|>". I want it to print [abc, <def>, ghi]. Is there a way to work some regex magic to accomplish what I want here?

Perhaps a simpler example:

System.out.println(
    Arrays.deepToString(
        "Hello! Oh my!! Good bye!!".split("(?:!+)")
    )
);

This prints [Hello, Oh my, Good bye]. I want it to print [Hello!, Oh my!!, Good bye!!]. `.

回答1:

You need to take a look at zero width matching constructs:

(?=X)   X, via zero-width positive lookahead
(?!X)   X, via zero-width negative lookahead
(?<=X)  X, via zero-width positive lookbehind
(?<!X)  X, via zero-width negative lookbehind

回答2:

You can use \b (word boundary) as what to look for as it is zero-width and use that as the anchor for looking for < and >.

String s = "abc<def>ghi";
String[] bits = s.split("(?<=>)\\b|\\b(?=<)");
for (String bit : bits) {
  System.out.println(bit);
}

Output:

abc
<def>
ghi

Now that isn't a general solution. You will probably need to write a custom split method for that.

Your second example suggests it's not really split() you're after but a regex matching loop. For example:

String s = "Hello! Oh my!! Good bye!!";
Pattern p = Pattern.compile("(.*?!+)\\s*");
Matcher m = p.matcher(s);
while (m.find()) {
  System.out.println("[" + m.group(1) + "]");
}

Output:

[Hello!]
[Oh my!!]
[Good bye!!]

回答3:

Thanks to information from Cine, I think these are the answers I'm looking for:

System.out.println(
    Arrays.deepToString(
        "abc<def>ghi<x><x>".split("(?=<)|(?<=>)")
    )
); // [abc, <def>, ghi, <x>, <x>]


System.out.println(
    Arrays.deepToString(
        "Hello! Oh my!! Good bye!! IT WORKS!!!".split("(?<=!++)")
    )
); // [Hello!,  Oh my!!,  Good bye!!,  IT WORKS!!!]

Now, the second one was honestly discovered by experimenting with all the different quantifiers. Neither greedy nor reluctant work, but possessive does.

I'm still not sure why.

来源：https://stackoverflow.com/questions/2406633/can-you-use-zero-width-matching-regex-in-string-split

标签

java

regex

split

delimiter