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Re: Self-updating relationship

Cross-posted to 2 groups.

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On 09/02/2015 07:28 PM, James Kuyper wrote:
> On 09/02/2015 07:13 PM, Stefan Ram wrote:
>> James Kuyper <jameskuyper@verizon.net> writes:
>>> Those both set spaces to 8, rather than height - number. If
>>> height-number is currently 8, that happens to be the right value, but
>>> isn't what I'm looking for.
>>
>>    If you just want to set »spaces« to »height - number« once,
>>    with no further update:
> ...
>>      final javafx.beans.property.IntegerProperty spaces
>>      = new javafx.beans.property.SimpleIntegerProperty
>>      ( height.getValue() - number.getValue() );
>
> So, using C++ as an analogy that I'm more familiar with, this constructs
> "spaces" as a SimpleIntegerProperty initialized with the value of that
> expression, which never gets re-evaluated.
>
> Your earlier version had:
>>      final javafx.beans.binding.NumberBinding spaces =
>>      height.subtract( number );
>
> which causes spaces.getValue() to behave like the equivalent of a C++
> member function whose return value is calculated using the specified
> formula freshly each time "spaces" is referred to. Is this a
> characteristic of binding.NumberBinding, or some more general Java feature?

It's a characteristic of the
javafx.beans.binding.Binding<T> interface.
<https://docs.oracle.com/javase/8/javafx/api/javafx/beans/binding/Binding.html>

Which depends upon the arguably more general
javafx.beans.Observable and
javafx.beans.value.ObservableValue<T> interfaces.

>
> Have I got that right?
>
> In C++, the equivalent of the first form above would be simpler than the
> equivalent of the second form, so it feels odd that the second form is
> simpler in Java. I'll try to keep that in mind should I ever need to
> program in Java again. It sounds like I've got a lot to learn before I
> even get started.
>

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Thread

Re: Self-updating relationship James Kuyper <jameskuyper@verizon.net> - 2015-09-02 17:14 -0400
  Re: Self-updating relationship Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-09-02 17:46 -0400
    Re: Self-updating relationship Arne Vajhøj <arne@vajhoej.dk> - 2015-09-03 21:06 -0400
      Re: Self-updating relationship e.d.programmer@gmail.com - 2015-09-04 04:46 -0700
        Re: Self-updating relationship Arne Vajhøj <arne@vajhoej.dk> - 2015-09-04 19:43 -0400
    Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-04 11:49 -0400
      Re: Self-updating relationship Arne Vajhøj <arne@vajhoej.dk> - 2015-09-04 19:45 -0400
        Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-04 22:10 -0400
          Re: Self-updating relationship Arne Vajhøj <arne@vajhoej.dk> - 2015-09-04 22:31 -0400
            Re: Self-updating relationship Arne Vajhøj <arne@vajhoej.dk> - 2015-09-04 22:38 -0400
            Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-04 22:51 -0400
  Re: Self-updating relationship James Kuyper <jameskuyper@verizon.net> - 2015-09-02 18:49 -0400
    Re: Self-updating relationship James Kuyper <jameskuyper@verizon.net> - 2015-09-02 19:28 -0400
      Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-02 23:52 -0400
        Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-03 10:32 -0400
          Re: Self-updating relationship James Kuyper <jameskuyper@verizon.net> - 2015-09-03 10:53 -0400
            Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-03 11:31 -0400
              Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-03 11:35 -0400
              Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-03 11:49 -0400
              Re: Self-updating relationship James Kuyper <jameskuyper@verizon.net> - 2015-09-03 12:16 -0400
                Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-03 13:03 -0400
          Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-03 10:55 -0400
      Re: Self-updating relationship James Kuyper <jameskuyper@verizon.net> - 2015-09-03 00:06 -0400
    Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-02 23:38 -0400
      Re: Self-updating relationship Jeff Higgins <jeff@invalid.invalid> - 2015-09-03 01:22 -0400

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