>>479
こんな感じだとどうだろうか？
import javax.xml.parsers.*;
import org.w3c.dom.*;
import java.util.*;
class TagNameExtractor {
public static void main(String[] args) throws Exception
{
HashSet<String> hs = new HashSet<String>();
DocumentBuilderFactory dbf=DocumentBuilderFactory.newInstance();
DocumentBuilder db= dbf.newDocumentBuilder();
Document doc = db.parse(System.in);
NodeList nl = doc.getElementsByTagName("*");
for(int i=0; i<nl.getLength(); i++){
hs.add(nl.item(i).getNodeName());
}
for(String s : hs){
System.out.println(s);
}
}
}