How do I express “:” but not preceded by “\” in a Java regular expression?

Question

How can I express \"not preceded by\" in a Java regular expression? For example I would like to search for \":\" but only when it is not directly preceded by \"\\\". How c

Answer 1

Use a negative lookbehind:

"(?

The reason for the four backslashes is:

• the backslash is a special character in regular expressions so you need the regular expression \\ to match a single backslash.
• backslashes must be escaped in Java strings, so each of the above backslashes must be written as \\, giving a total of four.

Example code:

Pattern pattern = Pattern.compile("(?

Output:

10