How to not include specific string in regex

Question

I need to build some kind of "java syntax" compiler in university. I want to use regex to match variable type and variable name (int num , String str etc.). So I need the regex to match one of the var types (String, int, char, boolean, double) and after that at least one space and var name, but var name CAN NOT be one of those types. How do I do that? I tried:

(String|int|char|boolean|double)[\s]+([a-zA-Z]+[\w]*^(String|int|char|boolean|double))

I know its not java regex syntax (only one '\' instead of two), but I tried this in http://regexpal.com/ and it doesn't work.

Thanks a lot!

Answer 1

A Negative Lookahead

^ will not work where you have it (it is an anchor that tries to assert that we are at the beginning of the string). But you were close, and if you just add ?! at the beginning of ethe parentheses that follow, it turns into a negative lookahead:

(String|int|char|boolean|double)\s+(?!(?:String|int|char|boolean|double)\b)[a-zA-Z]+

See demo

• Removed the brackets around \s and \w (unneeded).
• The negative lookbehind (?!(?:String|int|char|boolean|double)\b) asserts that what follows is not one of your types. If the assertion succeeds, the engine proceeds to match your var, specified by [a-zA-Z]+
• For more on lookarounds, see the reference section.

Reference

• Lookahead and Lookbehind Zero-Length Assertions
• Mastering Lookahead and Lookbehind