static S firstJavaToken(S s) {

  if (s == null) null;

  int l = s.length();

  int j = 0;

  char c, d;

  // scan for whitespace

  while (j < l) {

    c = s.charAt(j);

    d = j+1 >= l ? '\0' : s.charAt(j+1);

    if (c == ' ' || c == '\t' || c == '\r' || c == '\n')

      ++j;

    else if (c == '/' && d == '*') {

      do ++j; while (j < l && !s.substring(j, Math.min(j+2, l)).equals("*/"));

      j = Math.min(j+2, l);

    } else if (c == '/' && d == '/') {

      do ++j; while (j < l && "\r\n".indexOf(s.charAt(j)) < 0);

    } else

      break;

  }

  if (j >= l) null;

  int i = j;

  c = s.charAt(i);

  d = i+1 >= l ? '\0' : s.charAt(i+1);

  // scan for non-whitespace

  if (c == '\'' || c == '"') {

    char opener = c;

    ++j;

    while (j < l) {

      if (s.charAt(j) == opener || s.charAt(j) == '\n') { // end at \n to not propagate unclosed string literal errors

        ++j;

        break;

      } else if (s.charAt(j) == '\\' && j+1 < l)

        j += 2;

      else

        ++j;

    }

  } else if (Character.isJavaIdentifierStart(c))

    do ++j; while (j < l && (Character.isJavaIdentifierPart(s.charAt(j)) || "'".indexOf(s.charAt(j)) >= 0)); // for stuff like "don't"

  else if (Character.isDigit(c)) {

    do ++j; while (j < l && Character.isDigit(s.charAt(j)));

    if (j < l && s.charAt(j) == 'L') ++j; // Long constants like 1L

  } else if (c == '[' && d == '[') {

    do ++j; while (j+1 < l && !s.substring(j, j+2).equals("]]"));

    j = Math.min(j+2, l);

  } else if (c == '[' && d == '=' && i+2 < l && s.charAt(i+2) == '[') {

    do ++j; while (j+2 < l && !s.substring(j, j+3).equals("]=]"));

    j = Math.min(j+3, l);

  } else

    ++j;

  ret quickSubstring(s, i, j);

}