Java正则表达式匹配数学表达式模式

Question

I'm trying to match a string pattern like this recursively or iteratively.

term :- can be any variable(string) or integer
expression :- term + expression or term * expression or term / expression or term - expression

The idea is to find a matching pattern for mathematical expression like this

ZING^30*sin(45)+46*LENGTH-20

Let's assume that the term is ready.

As usual, I'll start from a very bad one... in java.

[[term\\+]*[term\\*]*[term\\\]*[term\\-]*]+term

Answer 1

You're using the wrong tool for the job. Regular expressions can't describe grammars with recursive syntaxes, by definition. Look up the Chomsky Hierarchy. You need an expression parser. Look up the Dijkstra Shunting-yard algorithm, or 'recursive descent expression parser'.

Answer 2

This looks like homework, so I'm not going to give you a complete answer. If you know how to use moderately complex regexes, you should be able to come up with a regex to represent your "term"--it shouldn't be too difficult. Now the regex for "expression" will be a term, followed by zero or more occurrences of "operator followed by term" (operator is one of + , - , * , / , maybe ^ ?). That is, expression will be "term", or "term op term", or "term op term op term", etc.

Note: this is how you'd write a regex that tells you whether the input has the correct format, but it won't help you break it down into parts. For that, you'd need a different regex (or two) that you would match in a loop. I can't tell just what your requirements are, though.