import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class RegExpExample {
public static void main(String args[]) {
String unadornedClassRE = "^\\s*class (\\w+)";
String doubleIdentifierRE = "\\b(\\w+)\\s+\\1\\b";
Pattern classPattern = Pattern.compile(unadornedClassRE);
Pattern doublePattern = Pattern.compile(doubleIdentifierRE);
Matcher classMatcher, doubleMatcher;
String line = " class MainClass";
classMatcher = classPattern.matcher(line);
doubleMatcher = doublePattern.matcher(line);
if (classMatcher.find()) {
System.out.println("The class [" + classMatcher.group(1) + "] is not public");
}
while (doubleMatcher.find()) {
System.out.println("The word \"" + doubleMatcher.group(1) + "\" occurs twice at position "
+ doubleMatcher.start());
}
}
}