Question

In this statement, taken from the Pagerank source code:

Pattern.compile("\\[.+?\\]");

What does the pattern mean? I have tried studying it, it says 2 slashes mean a single slash, but what are the .+??

Answer 1

This string literal:

"\\[.+?\\]"

means this string:

\[.+?\]

So this expression:

Pattern.compile("\\[.+?\\]");

means this regex:

\[.+?\]

which means “a literal [, followed by one or more characters — preferably as few as possible — followed by ]“. (. means “any character other than newline”; +? means “one or more of what I just said, and preferably as few as possible”.) So overall, the regex matches [____], where ____ can be anything that doesn’t contain a newline, as long as it’s at least one character long; and where ____ won’t (normally) contain a ] except possibly as the very first character.

For more information about Pattern and regexes in Java, see the documentation for the Pattern class.