[TF002] dot-star matches all strings! (true/false?)

(true/false?) In regex, the dot metacharacter matches everything, and the star allows zero or more repetition, so for all s instanceof String, s.matches(".*").

static void tf002(String s) {
   if (s instanceof String) {
      assert s.matches(".*");
   }
}

---

FALSE! From the Pattern API:

The regular expression . matches any character except a line terminator unless the DOTALL flag is specified.

tf002("\n"); // throws AssertionError

The correct statement is that for all s instanceof String, s.matches("(?s).*"). Note that (?s) is the embedded flag expression for Pattern.DOTALL.

Interestingly, Bug# 6565414 requests that .* be optimized since it "is always going to be true". The above counterproof demonstrates that this is incorrect: it's only trivially true in the so-called "single-line" mode.