The most efficient way to search a large String

Question

Hi All,
2 Quick Questions
QUESTION 1:
I have about 50 String keywords -- I would like to use to search a big String object (between 300-3000 characters)
Is the most efficient way to search it for my keywords like this ?
if(myBigString.indexOf("string1")!=1 || myBigString.indexOf("string2")!=1 || myBigString.indexOf("string1")!=1 and so on for 50 strings.)
System.out.println("it was found");
QUESTION 2:
Can someone help me out with a regular expression search of phone number in the format NNN-NNN-NNNN
I would like it to return all instances of that pattern found on the page .
I have done regular expressions, in javascript in vbscript but I have never done regular expressions in java.
Thanks

Answer 1

Answer 2:
If you have the option of using Java 1.4, have a look at the new regular expressions library... whose package name I forget :-/ There have been articles published on it, both at JavaWorld and IBM's developerWorks.
If you can't use Java 1.4, have a look at the jakarta regular expression projects, of which I think there are two (ORO and Perl-like, off the top of my head)
http://jakarta.apache.org/
Answer 1:
If you have n search terms, and are searching through a string of length l (the haystack, as in looking for a needle in a haystack), then searching for each term in turn will take time O(n*l). In particular, it will take longer the more terms you add (in a linear fashion, assuming the haystack stays the same length)
If this is sufficient, then do it! The simplest solution is (almost) always the easiest to maintain.
An alternative is to create a finite state machine that defines the search terms (Or multiple parallel finite state machines would probably be easier). You can then loop over the haystack string a single time to find every search term at once. Such an algorithm will take O(n*k) time to construct the finite state information (given an average search term length of k), and then O(l) for the search. For a large number of search terms, or a very large search string, this method will be faster than the naive method.
One example of a state-search for strings is the Boyer-Moore algorithm.
http://www-igm.univ-mlv.fr/~lecroq/string/tunedbm.html
Regards, and have fun,
-Troy