import com.sun.org.apache.xml.internal.utils.XMLCharacterRecognizer; //导入依赖的package包/类
/**
 * Convert a string to a double -- Allowed input is in fixed
 * notation ddd.fff.
 *
 * %OPT% CHECK PERFORMANCE against generating a Java String and
 * converting it to double. The advantage of running in native
 * machine code -- perhaps even microcode, on some systems -- may
 * more than make up for the cost of allocating and discarding the
 * additional object. We need to benchmark this.
 *
 * %OPT% More importantly, we need to decide whether we _care_ about
 * the performance of this operation. Does XString.toDouble constitute
 * any measurable percentage of our typical runtime? I suspect not!
 *
 * @return A double value representation of the string, or return Double.NaN
 * if the string can not be converted.  */
public double toDouble()
{
  if(m_length == 0)
    return Double.NaN;
  int i;
  char c;
  String valueString = fsb().getString(m_start,m_length);

  // The following are permitted in the Double.valueOf, but not by the XPath spec:
  // - a plus sign
  // - The use of e or E to indicate exponents
  // - trailing f, F, d, or D
  // See function comments; not sure if this is slower than actually doing the
  // conversion ourselves (as was before).

  for (i=0;i<m_length;i++)
    if (!XMLCharacterRecognizer.isWhiteSpace(valueString.charAt(i)))
      break;
  if (i == m_length) return Double.NaN;
  if (valueString.charAt(i) == '-')
    i++;
  for (;i<m_length;i++) {
    c = valueString.charAt(i);
    if (c != '.' && (c < '0' || c > '9'))
      break;
  }
  for (;i<m_length;i++)
    if (!XMLCharacterRecognizer.isWhiteSpace(valueString.charAt(i)))
      break;
  if (i != m_length)
    return Double.NaN;

  try {
    return Double.parseDouble(valueString);
  } catch (NumberFormatException nfe) {
    // This should catch double periods, empty strings.
    return Double.NaN;
  }
}
 

import com.sun.org.apache.xml.internal.utils.XMLCharacterRecognizer; //导入依赖的package包/类
/**
 * Returns whether the specified <var>ch</var> conforms to the XML 1.0 definition
 * of whitespace.  Refer to <A href="http://www.w3.org/TR/1998/REC-xml-19980210#NT-S">
 * the definition of <CODE>S</CODE></A> for details.
 * @param   ch      Character to check as XML whitespace.
 * @return          =true if <var>ch</var> is XML whitespace; otherwise =false.
 */
private static boolean isSpace(char ch)
{
  return XMLCharacterRecognizer.isWhiteSpace(ch);  // Take the easy way out for now.
}