For what it's worth, I agree with Larry and Landon.
Worst case scenario: code behaves badly and for some reason writes and rewrites
attributes on loading. Nobody knows of any code that does this, so it is an
edge use case. The price of doing this non-standard loading will be to write
back to the database unchanged data. That won't break anything, just make bad
coding run slower. On the plus side, we only have to store one boolean per
feature for all use cases and there will be a simplified way to mark features
as dirty or check a feature's dirty status.
--Christopher
--- On Thu, 4/30/09, Sunburned Surveyor <sunburned.surve...@gmail.com> wrote:
> From: Sunburned Surveyor <sunburned.surve...@gmail.com>
> Subject: Re: [JPP-Devel] Modifying BasicFeature to track modifications
> To: "OpenJump develop and use" <jump-pilot-devel@lists.sourceforge.net>
> Date: Thursday, April 30, 2009, 7:30 AM
> Larry wrote: "I appreciate all of the
> clever solutions, but I will
> remain convinced that BasicFeature can detect modification
> without any
> need for explicit client methods to set it, until someone
> shows me
> proof that it can not."
>
> I agree with Larry on this point. I believe it would be
> safe to
> develop a solution in which we assume each attribute is set
> only once
> during initialization, and not set and then reset during
> the
> initialization process. It may be true that this rule does
> not apply,
> but I think that would be an "edge case" and I can't think
> of any
> existing code in the core that would do this.
>
> On the other hand, if we require client code to call some
> type of
> "setInitComplete" method we are going to break all sorts of
> stuff. I
> would think this would require that all code in plug-ins
> and the core
> that create BasicFeature objects would have to be modified
> if the
> system was going to work as desired. That is a major
> refactoring.
>
> I think we should move forward with an internal mechanism
> to monitor
> modification of attribute values based on the assumption
> that
> attribute values are set once during initialization. This
> has a
> relatively low memory requirement, and if it doesn't work
> we will soon
> know about it.
>
> I will start work on this solution on my lunch break today
> if there
> are no objections. Perhaps the best way to end debate is
> with some
> code we all can test.
>
> The Sunburned Surveyor
>
> On Thu, Apr 30, 2009 at 6:33 AM, Larry Becker <becker.la...@gmail.com>
> wrote:
> > An example of the standard usage pattern for JDBC can
> be seen in:
> >
> com.vividsolutions.jump.datastore.jdbc.ValueConverterFactory.
> Regardless of
> > whether you use ResultSet's getObject() or something
> like getInt(),
> > eventually you are going to need an object
> representation of the data in
> > order to work with it. BasicFeature.SetAttribute
> requires an Object. So if
> > you did something like: new
> Integer(rs.getInt(columnIndex)) on a null column
> > , the JavaDoc for ResultSet says you'll get a zero int
> wrapped in an
> > Integer.
> >
> > I appreciate all of the clever solutions, but I will
> remain convinced that
> > BasicFeature can detect modification without any need
> for explicit client
> > methods to set it, until someone shows me proof that
> it can not.
> >
> > regards,
> > Larry
> >
> >
> > On Thu, Apr 30, 2009 at 6:24 AM, Paolo Rizzi <g...@oicom.com>
> wrote:
> >>
> >> The previous sample code I posted was foolish, I'm
> sorry!!!
> >>
> >> Find attached a better version that uses a single
> Object reference to
> >> track both initialization and modify state.
> >>
> >> During initialization this Object references a
> byte[] where each element
> >> tracks the init state of the corresponding
> attribute.
> >>
> >> Init ends when all attributes has been set at
> least once or when the
> >> client code calls a provided method.
> >>
> >> After init has ended the byte[] is discarded and
> the Object references the
> >> static instance of Boolean.FALSE (so there's no
> memory wasted beyound the
> >> single Object reference itself).
> >>
> >> After at least one attributes is set, the Object
> references the static
> >> instance Boolean.TRUE.
> >>
> >> Client code can decide to force init end with a
> non-modified state or even
> >> an already-modified state, if it likes to.
> >>
> >> The code does not check if the new value set for
> an attribute is equal or
> >> not to the value already present. This is because
> a == check would not be
> >> good because two different Integer instances both
> containing the same value
> >> are to be considered equal.
> >> So the equals() method should be used, but that is
> not garanteed to work
> >> with all class types, so I think it may be better
> to skip the check
> >> altogether and consider an attribute modified in
> any case.
> >>
> >> Hope this is helpful!!! :-)
> >>
> >> Bye
> >> Paolo
> >>
> >>
> >>
> >> public class BasicFeature {
> >> private Object[] attributes;
> >> private Object mods;
> >>
> >> public void forceInitEnded(boolean
> modified) {
> >> //force init end and specified
> modify state
> >> mods = modified ? Boolean.TRUE :
> Boolean.FALSE;
> >> }
> >>
> >> public boolean isInitEnded() {
> >> if( mods instanceof Boolean )
> //init ended
> >> return true;
> >>
> >> if( mods == null ) {
> //if still
> >> null
> >> mods = new
> byte[attributes.length]; //create it
> >>
> Arrays.fill((byte[])mods,(byte)0); //fill with
> zeros
> >>
> >> return false; //init not even
> started
> >> }
> >>
> >> for(int
> i=0;i<((byte[])mods).length;i++)
> >> if( ((byte[])mods)[i] == 0 )
> //if any attribute never flagged
> >> return false;
> //init not ended
> >>
> >> forceInitEnded(false);
> //init ended, no mods done
> >>
> >> return true; //init ended
> >> }
> >>
> >> public void setAttribute(Object[]
> newAttributes) {
> >> //call setAttribute() for each
> element
> >> }
> >>
> >> public void setAttribute(int
> attributeIndex, Object newAttribute) {
> >> if( isInitEnded() )
> //if init ended
> >> mods = Boolean.TRUE;
> //feature modified
> >> else
> >>
> >> //if init not ended
> >> ((byte[])mods)[attributeIndex] =
> 1; //flag the attributes
> >> mod
> >>
> >> attributes[attributeIndex] =
> newAttribute;
> >> }
> >>
> >> public boolean isModified() {
> >> return isInitEnded() ?
> ((Boolean)mods).booleanValue() : false;
> >> }
> >> }
> >>
> >>
> >>
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> >
> >
> >
> > --
> > http://amusingprogrammer.blogspot.com/
> >
> >
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