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Re: Proposal
- From: Jean-Marie Dautelle <
>
- To:
- Subject: Re: Proposal
- Date: Sun, 2 Nov 2014 11:47:43 +0100
Actually, they are useful as a general contract for sub-interfaces to make
sure there is always consistency between a quantity unit and the quantity
itself. They also simplify the sub-interface definition (no need to
override add, subtract, times(Number).
public interface Quantity<Q extends Quantity> {
Unit<Q> unit();
...
Quantity<Q> add(Quantity<Q>);
...
}
On Sun, Nov 2, 2014 at 11:27 AM, Otávio Gonçalves de Santana <
>
wrote:
>
I think it is cool, so we need to work with the specific interface, so the
>
generics in Quantity, don't make more sense, so we could remove it too.
>
>
On Sun, Nov 2, 2014 at 8:15 AM, Jean-Marie Dautelle
>
<
>
>
wrote:
>
>
> Or better:
>
>
>
> // Unit-API
>
> interface QuantityFactory<N extends Number> {
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> Length lengthOf(N, Unit<Length>);
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> Mass massOf(N, Unit<Length>);
>
> ...
>
> }
>
> // Unit RI
>
> abstract class Quantities {
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> public static QuantityFactory<Double> DOUBLE = ...;
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> public static QuantityFactory<BigDecimal> BIG_DECIMAL = ...;
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> }
>
>
>
>
>
> On Sun, Nov 2, 2014 at 11:11 AM, Jean-Marie Dautelle
>
> <
>
>
> wrote:
>
>
>
>> Erratum:
>
>>
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>> / Unit-API
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>> interface QuantityFactory {
>
>> Length lengthOf(Number, Unit<Length>);
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>> Mass massOf(Number, Unit<Length>);
>
>> ...
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>> }
>
>>
>
>>
>
>> On Sun, Nov 2, 2014 at 10:50 AM, Jean-Marie Dautelle
>
>> <
>
>> > wrote:
>
>>
>
>>> Hello all,
>
>>>
>
>>> I understand your points, but I have the feeling that we are making
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>>> things more difficult than they need to be.
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>>>
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>>> We should not forget that the main subject is the unit-api not the
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>>> "quantity-api".
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>>>
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>>> Let's put ourselves in the shoes of the user and see what he might want
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>>> to do:
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>>>
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>>> public void wait(Time delay) { ... }
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>>> Mass m = parcel.getWeight();
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>>>
>
>>> I would assume that until that point everyone agree... [?]
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>>>
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>>> Let's go deeper, we might want to do also:
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>>>
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>>> Length x = ...
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>>> Time t = ...
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>>> Velocity v = x.divide(t);
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>>>
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>>> If we can do that then I believe that even more people will be happy
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>>> (especially if it does not involve reflection) [?]
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>>>
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>>> ... And YES, it is possible!
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>>>
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>>> The first thing we see is that some of the quantities interfaces will
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>>> have extra methods.
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>>>
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>>> interface Length extends Quantity<Length> {
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>>> Area multiply(Quantity<Length>); // Overloading.
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>>> }
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>>> interface Area extends Quantity<Area> {
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>>> Volume multiply(Quantity<Length>); // Overloading.
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>>> }
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>>> Length x = ...
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>>> Volume v = x.multiply(x).multiply(x);
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>>>
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>>> There is no combination explosion since the number of predefined
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>>> quantities is bounded. Furthermore, all these are convenient (optional)
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>>> methods, the asType(Class<Q>) method can be used for complex cases.
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>>>
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>>> The question now is how do we create these Quantity instances?
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>>>
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>>> For this problem, the abstract factory pattern (GoF) is a perfect fit.
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>>> All quantities coming from the same factory will work well together and
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>>> this approach allows for many many optimizations under the hood !
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>>>
>
>>> // Unit-API
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>>> interface QuantityFactory {
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>>> Length lengthOf(double, Unit<Length>);
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>>> Mass massOf(double, Unit<Length>);
>
>>> ...
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>>> }
>
>>>
>
>>> // Unit RI
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>>> abstract class Quantities {
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>>> public static QuantityFactory DOUBLE = ...;
>
>>> public static QuantityFactory BIG_DECIMAL = ...;
>
>>> }
>
>>>
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>>> Length x = DOUBLE.lengthOf(2.4, METER);
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>>> Length two_x = x.add(x);
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>>> Area x_square = x.multiply(x);
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>>>
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>>> (Note: I would have preferred plus, minus, time, divide but I can live
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>>> with that [?])
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>>>
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>>> There is no need for a Measurement class (and MeasurementConverter).
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>>>
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>>> The quantity base class will be very close to what we have now except
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>>> it does not implement any interface.
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>>>
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>>> public interface Quantity<Q extends Quantity> {
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>>> Unit<Q> unit();
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>>> Number value();
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>>> double doubleValue(Unit<Q>); // To avoid boxing/deboxing.
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>>> Quantity<Q> add(Quantity<Q>);
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>>> ...
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>>> }
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>>>
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>>> Of course if we can converge on this solution I would be really really
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>>> happy (JScience has many types of numbers such as Rational, Complex for
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>>> which this approach is a perfect fit) !!!
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>>>
>
>>> Best regards,
>
>>> Jean-Marie.
>
>>>
>
>>
>
>>
>
>>
>
>> --
>
>> It is not the strongest of the species that survives, nor the most
>
>> intelligent. It is the one that is most adaptable to change. - Darwin's
>
>> Origin of Species (digest)
>
>>
>
>
>
>
>
>
>
> --
>
> It is not the strongest of the species that survives, nor the most
>
> intelligent. It is the one that is most adaptable to change. - Darwin's
>
> Origin of Species (digest)
>
>
>
>
>
>
--
>
Otávio Gonçalves de Santana
>
>
blog: http://otaviosantana.blogspot.com.br/
>
twitter: http://twitter.com/otaviojava
>
site: *http://about.me/otaviojava <http://about.me/otaviojava>*
>
55 (11) 98255-3513
>
>
--
It is not the strongest of the species that survives, nor the most
intelligent. It is the one that is most adaptable to change. - Darwin's
Origin of Species (digest)
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