import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Main {
public static void main(String args[]) throws Exception {
String duplicatePattern = "\\b(\\w+) \\1\\b";
Pattern p = Pattern.compile(duplicatePattern);
int matches = 0;
String phrase = "this is a test";
Matcher m = p.matcher(phrase);
String val = null;
while (m.find()) {
val = ":" + m.group() + ":";
System.out.println(val);
matches++;
}
}
}