Re: How to deal with empty string when reading input from a file?

Patricia Shanahan <>
Wed, 02 May 2007 07:30:07 -0700
www wrote:

Gordon Beaton wrote:

Separate the trim() from the valueOf(), and use the default value when
trim() results in an empty string:

  double doubleOrZero(String s) throws NumberFormatException {
    String trimmed = s.trim();

    if ("".equals(trimmed)) {
      return 0.0;
    else {
      return Double.valueOf(trimmed);


  double value = doubleOrZero(line1.substring(0,25));
  double valueB = doubleOrZero(line1.substring(30,45));


Thank you. I was surprised that, why Double.valueOf("") is not 0.0?
instead it throws an Exception!
Could you help me a little more? Thank you.

The simple answer is just that those are the rules - see the
Double.valueOf documentation,

However, you probably want to know why those are the rules.

I don't think there is any one-size-fits-all right answer to the
handling of an empty string, or an all space string. In that sort of
situation, it is usually better to err on the side of reporting the
problem, to bring it to the programmer's attention. The programmer can
then decide the right handling on a case-by-case basis.

Incidentally, Double.valueOf ignores leading and trailing whitespace, so
normally there is no need to trim. However, in this case it simplifies
the all space test.


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