Prev: Integrating Google Maps in Java Swing application
Next: Swing JDialog wrong cursor shapes
From: Rhino on 17 May 2010 12:54
Lew <lew(a)lewscanon.com> wrote in
news:ff80f694-2246-4ed4-b7d8-d5c6a8fd06b1(a)f13g2000vbm.googlegroups.com:

> Rhino wrote:
>> 1. If I create a JSpinner with a SpinnerNumberModel and specify the
>> numbers in the model explicitly as short, why can't I rely on the
>> getValue() from the JSpinner always returning shorts? In other words,
>> if I define it all
>
> Because that is not the defined behavior of the model.
>
>> with shorts, what actions on my part will result in getValue()
>> returning an Integer or something other than Short? For some reason,
>> the results from
>>
>
> I don't know, but I bet if you look at the source for
> 'SpinnerNumberModel' you'll find out. My guess is that it uses the
> subtype of 'Number' that most closely matches the returned value.
>
> Given the model class's contract, there's nothing you can do directly
> to change what it returns. You get a 'Number' and that's the best you
> can predict.
>
>> getValue() are sometimes Short but sometimes Integer and I don't
>> understand why. I'm trying to figure out how to make getValue()
>> return ONLY Short (or, failing that, to return only Integer.) This is
>> the statement that defined the model:
>>
>> SpinnerNumberModel seasonNumberModel = new
>> SpinnerNumberModel((short)1, (short)1, (short)20, (short)1);
>>
>
> This call feeds integers to the constructor. Did you look at the
> Javadocs for the constructor? You are taking 'int' values, casting
> them to 'short', then the language is widening them back to 'int'
> arguments. There is no constructor overload for that class that takes
> 'short' parameters.
>
Casting the input parameters to short was my naive attempt to force
SpinnerNumberModel to use shorts instead of ints. It's now obvious to me
that this would never work.

> All you are guaranteed from 'SpinnerNumberModel' is that the returned
> value of 'getValue()' is a 'Number'. (The signature says 'Object',
> but the Javadocs tell you that it will be a 'Number'.) If you want
> different behavior, set your own model.
>
I may do that but it's probably not necessary in this case.

>> 2. If a given method can return various sorts of integer numbers,
>> like Short, Integer, and Long, what is the simplest way to determine
>> the exact type that is being returned by the method? I'm just trying
>> to cover the
>>
>
> Don't.
>
> Just use the return type, which for 'SpinnerNumberModel' is an
> 'Object' that can be downcast to 'Number'.
>
>> worst-case scenario that factors beyond my control may make it
>> impossible to predict whether getValue() is going to return Integer
>> or Short from my JSpinner. If that turns out to be true, I'd like to
>> know the best way to determine if a given value is a short, int, long
>> or anything else. I think I used to know how to do that several years
>> ago but I'm darned if I can remember that technique now.
>>
>
> 'instanceof'?
>
> What difference does it make? Just use 'Number'. Use its
> 'longValue()', 'intValue()', etc., methods if you must.
>
> You're making a mountain out of a molehill. Read the Javadocs for the
> classes and methods you're using! They will tell you what guarantees
> you can count on, and that's all you get to count on. Live with it.
>
Fair enough. I did look at the Javadocs but didn't read the main comments
for the class very carefully and just went straight to the method
signatures so that's why I missed that "Numbers" are returned by the
class.

The classes I am writing are basically editing rows of a database table.
Three of the six columns of the table are defined as SMALLINT - I'm using
DB2 - and SMALLINT corresponds to short in Java. Each of those three
short columns contains only a small range of integers in the range of 1
to 3 or 1 to 20. While my main display of the data is in the form of a
JTable, I have written insert/update/delete dialogs for the table. Those
dialogs use JSpinners to present those numbers and limit what values
users can choose for them.

It seemed to make sense that if I gave the spinner number model shorts,
shorts would be returned by getValue(). I see now - thanks to your reply
- that I have misunderstood how this class is supposed to work.

I need to rethink the formats I am using for my data throughout my
classes. The data that comes in as a short is apparently going to be an
integer within the spinner and then need to be changed back to a short
for writing to the database during an insert or update.

Eventually, I may edit the data directly in the JTable; the
insert/udpdate/delete dialogs are just a "quick and dirty" temporary
expedient.

Thanks for helping me set more realistic expectations for the spinner
number model.
--
Rhino
From: Lew on 17 May 2010 14:48
Rhino wrote:
> It seemed to make sense that if I gave the spinner number model shorts,
> shorts would be returned by getValue().
>

You could use the SpinnerNumberModel 'getNumber().shortValue()' method
chain and get a 'short' value directly.

If the actual values fall outside the 'short' range you could get
bizarre results, but that presumably is handled by how you set up the
spinner's values.

--
Lew
From: Rhino on 17 May 2010 18:31
Eric Sosman <esosman(a)ieee-dot-org.invalid> wrote in
news:hsrndj$onk$1(a)news.eternal-september.org:

> On 5/17/2010 8:37 AM, Rhino wrote:
>> 1. If I create a JSpinner with a SpinnerNumberModel and specify the
>> numbers in the model explicitly as short, why can't I rely on the
>> getValue() from the JSpinner always returning shorts? In other words,
>> if I define it all with shorts, what actions on my part will result
>> in getValue() returning an Integer or something other than Short? For
>> some reason, the results from getValue() are sometimes Short but
>> sometimes Integer and I don't understand why. I'm trying to figure
>> out how to make getValue() return ONLY Short (or, failing that, to
>> return only Integer.) This is the statement that defined the model:
>>
>> SpinnerNumberModel seasonNumberModel = new
>> SpinnerNumberModel((short)1, (short)1, (short)20, (short)1);
>
> This is just like `new SpinnerNumberModel(1, 1, 20, 1)' -- the
> fact that your promoted-to-int arguments happen to be in range for
> `short' (or even for `byte') doesn't influence the constructor's
> behavior, nor that of the constructed SpinnerNumberModel.
>
Yes, Lew and RedGrittyBrick have already set me straight on that. Let's
just say I was very naive about use of the SpinnerNumberModel and leave
it at that ;-)

> Also, even if the supposed range of the SpinnerNumberModel is
> 1 through 20 with an integer step, setValue(new Double(98.6)) is
> still possible and will work.

That's a bit surprising! It's not desireable in this case so I won't let
anyone do it programmatically but I suppose it might be desireable in
some cases.....
>
> It's a little odd that you use getValue() instead of getNumber(),
> but that shouldn't matter a lot.

My goodness! I missed the getNumber() method altogether! Maybe I'll
switch to that....
>
>> 2. If a given method can return various sorts of integer numbers,
>> like Short, Integer, and Long, what is the simplest way to determine
>> the exact type that is being returned by the method? I'm just trying
>> to cover the worst-case scenario that factors beyond my control may
>> make it impossible to predict whether getValue() is going to return
>> Integer or Short from my JSpinner. If that turns out to be true, I'd
>> like to know the best way to determine if a given value is a short,
>> int, long or anything else. I think I used to know how to do that
>> several years ago but I'm darned if I can remember that technique
>> now.
>
> You can use getClass() or instanceof on the returned Object().
> If you really want to be draconian, you could do
>
> Number num = seasonNumberModel.getNumber();
> if (! (num instanceof Short)) {
> // Accept no substitutes:
> num = Short.valueOf(num.shortValue());
> }
>
Is there any way to do the same thing with a primitive? Mind you, I'm
having trouble thinking of a case when you'd need to! In the case of
SpinnerNumberModel, I now know that I'm getting a Number, which may
actually be a Short, Integer, Long, etc. and I can determine which I'm
getting via instanceof or getClass(). If a method is capable of returning
several different primitives - and I don't know of any that is offhand -
how could I tell if it was giving me an int, long, short, double or
whatever?

--
Rhino


--
Rhino
From: Lew on 17 May 2010 19:14
On 05/17/2010 01:09 AM, Rhino wrote:
> When you construct a JSpinner with a SpinnerNumberModel, what is the
> datatype of the numbers in the model?

Please do not multipost.

--
Lew
From: RedGrittyBrick on 18 May 2010 05:25
On 17/05/2010 23:31, Rhino wrote:
> If a method is capable of returning [one of] several different primitives

That isn't possible in Java. The type of return value is part of a
method signature. If it is returning a primitive type, covariance
doesn't apply.

--
RGB
First  |  Prev  |  Next  |  Last
Pages: 1 2 3
Prev: Integrating Google Maps in Java Swing application
Next: Swing JDialog wrong cursor shapes