需要帮助用正则表达式拆分表达式

Question

I have an expression like this.

A AND (B OR (C OR D))

I want the parentheses as a separate string and not combined with C OR D in the output array.

[A, AND, (, B, OR, (, C, OR, D, ), )]

Appending , in place of SPACE and after every ( and before every ) and then using .split(",") would solve my problem.

Is there any way better way to do this by simply using the right regex in the split method ?

Answer 1

How about this:

String input = "A AND (B OR (C OR D))";
String regex = "\\s+|(?<=\\()|(?=\\))";
String[] tokens = input.split(regex);

Which returns:

{A, AND, (, B, OR, (, C, OR, D, ), )}

Explanation:

The regex splits by

• One or more spaces
• Anything followed by a parenthesis
• Anything preceded by a parenthesis

I used positive lookaheads and positive lookbehinds, which are INCREDIBLY useful, so do look them up (no pun intended)

Answer 2

I hope this would help:

"A AND (B OR (C OR D))".split(" +| (?=\\()|(?=\\))|(?<=\\()") #=> [A, AND, (, B, OR, (, C, OR, D, ), )]

 + # splits by whitespaces
 (?=\\() # splits by whitespace followed by opening brace: e.g. in " (" it would give you single "(" instead of " " and "(" (like in the next part without whitespace in the beginning)
(?=\\)) # splits by empty string followed by closing brace: e.g. "B)" => ["B", ")"]
(?<=\\)) # splits by empty string preceding by closing brace: e.g. "))"

Search for "Positive lookahead/lookbehind" in regular expressions (personally I use regex101.com).