Regex in java for finding duplicate consecutive words

Question

I saw this as an answer for finding repeated words in a string. But when I use it, it thinks This and is are the same and deletes the is

Answer 1

Try this one:

String pattern = "(?i)\\b([a-z]+)\\b(?:\\s+\\1\\b)+";
Pattern r = Pattern.compile(pattern, Pattern.CASE_INSENSITIVE);

String input = "your string";
Matcher m = r.matcher(input);
while (m.find()) {
    input = input.replaceAll(m.group(), m.group(1));
}
System.out.println(input);

The Java regular expressions are explained very well in the API documentation of the Pattern class. After adding some spaces to indicate the different parts of the regular expression:

"(?i) \\b ([a-z]+) \\b (?: \\s+ \\1 \\b )+"

\b       match a word boundary
[a-z]+   match a word with one or more characters;
         the parentheses capture the word as a group    
\b       match a word boundary
(?:      indicates a non-capturing group (which starts here)
\s+      match one or more white space characters
\1       is a back reference to the first (captured) group;
         so the word is repeated here
\b       match a word boundary
)+       indicates the end of the non-capturing group and
         allows it to occur one or more times