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From: James Kuyper <jameskuyper@verizon.net>
Newsgroups: comp.lang.c,comp.lang.java.programmer
Subject: Re: Self-updating relationship
Date: Thu, 3 Sep 2015 12:16:48 -0400
Organization: A noiseless patient Spider
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References: <relationship-20150902211808@ram.dialup.fu-berlin.de> <55E766BD.3060303@verizon.net> <spaces-20150902222406@ram.dialup.fu-berlin.de> <55E77D04.6080200@verizon.net> <properties-20150903001216@ram.dialup.fu-berlin.de> <55E78636.5000908@verizon.net> <ms8g5j$o5k$1@dont-email.me> <ms9llv$pto$1@dont-email.me> <ms9mpb$srk$1@dont-email.me> <ms9p30$8vc$1@dont-email.me>
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On 09/03/2015 11:31 AM, Jeff Higgins wrote:
> On 09/03/2015 10:53 AM, James Kuyper wrote:
>> On 09/03/2015 10:32 AM, Jeff Higgins wrote:
>>> On 09/02/2015 11:52 PM, Jeff Higgins wrote:
>>>> On 09/02/2015 07:28 PM, James Kuyper wrote:
>>>
>>>>> 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>
>>>>
>>>
>>> Sorry, this is incorrect.
>>> It's a characteristic of the
>>> javafx.beans.property.Property<T> interface.
>>> <https://docs.oracle.com/javase/8/javafx/api/javafx/beans/property/Property.html>
>>
>> According to Stefan Ram, using the following code:
>>>      final javafx.beans.binding.NumberBinding spaces =
>>>      height.subtract( number );
>>
>> would cause the subtraction to be re-evaluated with the current values
>> of height and number, each time spaces.getValue() is called, while
> 
> Correct.
> 
>>
>>
>>>      final javafx.beans.property.IntegerProperty spaces
>>>      = new javafx.beans.property.SimpleIntegerProperty
>>>      ( height.getValue() - number.getValue() );
>>
>> would cause the subtraction to be performed only once, when spaces is
>> created. Are you saying he got those reversed?
> 
> No.

OK - I thought I was beginning to understand  what was going on, but now
I'm thoroughly confused. You're saying that this behavior (Specifically,
the behavior of re-calculating the subtraction each time
spaces.getValue() is used) is a property of the
javafx.beans.property.Property<T> interface, rather than a property of
the javafx.beans.binding.Binding<T> interface, despite the fact that it
happens when he uses javafx.beans.binding.NumberBinding, and doesn't
happen when he uses javafx.beans.property.SimpleIntegerProperty?

How does that work? Does javafx.beans.binding.NumberBinding use
javafx.beans.property.Property<T> while
javafx.beans.property.SimpleIntegerProperty uses
javafx.beans.binding.Binding<T>? That's not at all what I would have
expected, based solely upon the names.


-- 
James Kuyper