Tokenizing an infix string in Java

Question

I\'m implementing the Shunting Yard Algorithm in Java, as a side project to my AP Computer Science class. I\'ve implemented a simple one in Javascript, with only basic arith

Answer 1

Try .spliting on the regex

(?<=[^\.a-zA-Z\d])|(?=[^\.a-zA-Z\d])

It will split the string at any place that is either preceded or followed by a non-alphanumeric character or period.

• (?<=[^\.a-zA-Z\d]) is a positive lookbehind. It matches the place between two characters, if the preceding string matches the sub-regex contained within (?<=...).
  • [^\.a-zA-Z\d] is a negated character class. It matches a single character that is not contained within [^...].
    • \. matches the character ..
    • a-z matches any lowercase character between a and z.
    • A-Z is the same, but for uppercase.
    • \d is the equivalent of [0-9], so it matches any digit.
• | is the equivalent of an "or". It makes the regex match either the preceding half of the regex or the following half.
• (?=[^\.a-zA-Z\d]) is the same as the first half of the regex, except that it is a positive lookahead. It matches the place between two characters, if the following string matches the sub-regex contained within (?=...).

You can implement this regex in java like this:

String str = "sin(4+3)-8";
String[] parts = str.split("(?<=[^\\.a-zA-Z\\d])|(?=[^\\.a-zA-Z\\d])");

Result:

["sin","(" 4,"+",3,")","-","8"]