How do I check if a String contains the same letter more than once?

Question

I'm a bit confused in how I would check if a String contains the same letter more than once.

ArrayList<String> words = new ArrayList<String>();

words.add("zebra");
words.add("buzzer");
words.add("zappaz");

Let's say I only want to print out any words which contain more than one "z", therefore only "buzzer" and "zappaz" would get printed. How would I do this?

Answer 1

To test if a string contains two z, you can do this :

 boolean ok = word.matches(".*z.*z.*")

Answer 2

indexOf returns the... index of... a character in a string. It also takes an optional argument specifying where to search. If there is no match, it returns -1. So just use it twice:

s.indexOf(letter, s.indexOf(letter) + 1) > -1

It works!

(For efficiency's sake, though, may as well check the first result.)