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From: James Kuyper <jameskuyper@verizon.net>
Newsgroups: comp.lang.c,comp.lang.java.programmer
Subject: Re: Self-updating relationship
Date: Wed, 02 Sep 2015 19:28:54 -0400
Organization: Self
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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>
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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?

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.