Regular expression question with "any character except" condition in Java?

Question

Java

Why is the regular expression not working as intended?
Source string:
String source = "-1 - -2233 -3- -4";

Regular expression:
String NUMBER_INT_SEPARATOR = "[^-(?=\\d)]";

Splitting a string by regular expression will be done using the split() method of the String object .
For reference

The split() method splits the string around matches with the given regular expression.

Parsing a regular expression step by step:

• [^] - any character(s) other than the one that will be in square brackets.
  
• [^-] - any characters except dash (-) .
  
• x(?=y) - Matches 'x' only if 'x' is followed by 'y'. This is called preemption ( source ).
  
• [^-(?=\\d)] - any characters except a dash followed by a numeric character
  

Then the question is: why does this regular expression also capture a single dash character?

At the output we get:

-1
-
-2233
-3-
-4

Answer 1

x(?=y) - Matches 'x' only if 'x' is followed by 'y'. It's called preemption (source).

This is if this design was freestanding. But you have it enclosed in [], which means
[^] - any character (s) except for the one that will be in square brackets, that is, all characters except -, (, ?, \, d, )