Java Pattern Matching - can matched pattern be memorised and used later in the same regex?

Question

The program I am writing needs to ensure that it does not have a word or sequence of chars repeated in the input string.
How can I ensure this using java pattern matching? I think this is possible if regex can memorise the patterns it has found. Or may be I am wrong.
But ultimately I want to know if this is possible using java regex.

Ex:
goneishegone \\\\ should return true - "gone" has appeared twice.
goneisheyesterday \\\\ should return false - has not repeating words. (minimum length of words that repeat should be 2 or more)

Answer 1

You can add the words that your regex matches into a HashSet. If the add() Method returns false, the word is already in the Set. So your solultion would look something like the following:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

...

Boolean return = false;
Set<String> allMatches = new HashSet<String>();
Matcher m = Pattern.compile("your regular expression here")
    .matcher(yourStringHere);
while (m.find()) {
  if(!allMatches.add(m.group())){
    return = true;
    break;
}

System.out.println(Boolean.toString(return));