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From: Jeff Higgins <jeff@invalid.invalid>
Newsgroups: comp.lang.c,comp.lang.java.programmer
Subject: Re: Self-updating relationship
Date: Thu, 03 Sep 2015 11:31:02 -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>
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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.

I don't know if you saw my example elsewhere in this thread.
I think it is more clear than the example provided by Stefan.
Bringing NumberBinding into the example was unfortunate IMHO.

In it, the ability to bind/unbind becomes much easier.
Despite its name, to get NumberBinding to provide bind/unbind
capabilities you must do the work yourself. As recommended in
the NumberBinding javadoc this is best done by extending a
base class implementation such as DoubleBinding. See the
DoubleBinding javadoc for example code.