Shouldn't “static” patterns always be static?

Question

I just found a bug in some code I didn\'t write and I\'m a bit surprised:

Pattern pattern = Pattern.compile(\"\\\\d{1,2}.\\\\d{1,2}.\\\\d{4}\");
Matcher matc         


        

Answer 1

first, the bug in pattern is because dot (.) matches everything. If you want to match dot (.) you have to escape it in regex:

Pattern pattern = Pattern.compile("\\d{1,2}\\.\\d{1,2}\\.\\d{4}");

Second, Pattern.compile() is a heavy method. It is always recommended to initialize static pattern (I mean patterns that are not being changed or not generated on the fly) only once. One of the popular ways to achieve this is to put the Pattern.compile() into static initializer.

You can use other approach. For example using singleton pattern or using framework that creates singleton objects (like Spring).