Is it possible I found a bug in Java Pattern (JDK 1.5)???

Question

It is hard to believe that I should have found an error in the java.util.regex.Pattern class - and I hope you can tell me I'm wrong. Look at this example:
Let's say the pattern is "%\d+". I can then easily match against, let's say "%20". If I however changes the string to "%20 ", then no match, not complete or partial! The oddest thing is that it seems to be connected to the usage of "%". To really nail the point..if you change the string to "%20 %20 ", then you will find two partial matches (which is correct). I have tried to debug the Pattern-class myself - but my debugger wouldn't show me the local variables in the Pattern class, so I gave up. Try to run the program below with JRE 1.5 (update 18) and exchange the "s" var to test it.
public class RegExp {
private static Pattern pattern = Pattern.compile("%\\d+");
public static void main(String[] args) {
          String s = "%20";
          Matcher m = pattern.matcher(s);
          if (m.matches()) {
               System.out.println("Complete match:");
               for (int i = 0; i <= m.groupCount(); i++) {
                    System.out.println("Group " + i + " : " + m.group(i));
          } else if (m.find()) {
               int pos = 0;
               while (m.find(pos)) {
                    System.out.println("Partial match:");
                    pos = m.end();
                    for (int i = 0; i <= m.groupCount(); i++) {
                         System.out.println("Group " + i + " : " + m.group(i));
          } else {
               System.out.println("NO MATCH");
Edited by: mortensi on Jun 4, 2009 2:25 AM

Answer 1

Sorry about the code. It truly compiled and worked..but I didn't know about the code-tag thing. Here is an version that should work well...or at least I hope so
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class RegExp {
     private static Pattern pattern = Pattern.compile("%\\d+");
      * @param args
     public static void main(String[] args) {
          String s = "%20";
          Matcher m = pattern.matcher(s);
          if (m.matches()) {
               System.out.println("Complete match:");
               for (int i = 0; i <= m.groupCount(); i++) {
                    System.out.println("Group " + i + " : " + m.group(i));
          } else if (m.find()) {
               int pos = 0;
               while (m.find(pos)) {
                    System.out.println("Partial match:");
                    pos = m.end();
                    for (int i = 0; i <= m.groupCount(); i++) {
                         System.out.println("Group " + i + " : " + m.group(i));
          } else {
               System.out.println("NO MATCH");
}