code: String regExpGroupName(String pkgName) {
          for (int j = 0; j < sortedRegExpList.size(); j++) {
              String regexp = sortedRegExpList.get(j);
              if (pkgName.startsWith(regexp)) {
                  return regExpGroupMap.get(regexp);
              }
          }
          return null;
      }
docs: Search for package name in the sorted regular expression
  list, if found return the group name.  If not, return null.
  
  @param pkgName Name of package to be found in the regular
  expression list.