String.matches() question - regular expression help

Question

How come the following code's if condition returns false?
String someFile="Dr. Phil.pdf";
if (someFile.matches("[.][Pp][Dd][Ff]$")) {
  System.out.println("File is a pdf file.");
}When I change the the matches method to matches(".*[Pp][Dd][Ff]$") it works, so does that mean it has to match the entire string to return true? If so, how can I determine if a partial match occured?
If partial matching isn't feasible, then can someone help me look determine if this is the best matching pattern to use:
matches(".*[.][Pp][Dd][Ff]$")Thanks.

Answer 1

The documentation is your friend.
[String.matches(regex)|http://java.sun.com/javase/6/docs/api/java/lang/String.html#matches(java.lang.String)] says:
An invocation of this method of the form str.matches(regex) yields exactly the same result as the expression
Pattern.matches(regex, str)And [Pattern.matches(regex, str)|http://java.sun.com/javase/6/docs/api/java/util/regex/Pattern.html#matches(java.lang.String, java.lang.CharSequence)] says
behaves in exactly the same way as the expression
Pattern.compile(regex).matcher(input).matches()And [Matcher.matches()|http://java.sun.com/javase/6/docs/api/java/util/regex/Matcher.html#matches()] says
Attempts to match the entire region against the pattern.