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Re: Remove "generic" multiply/divide operations from Quantity
- From: Werner Keil <
>
- To:
- Subject: Re: Remove "generic" multiply/divide operations from Quantity
- Date: Fri, 17 Oct 2014 06:02:09 +0200
Nothing, it always worked as long as you subclass Unit (where there are
similar wildcard methods) or Quantity.
asType() which allows guidance (similar to a non-wildcard proposed) can be
tricked and tweaked any way you want, too.
Unit<InformationRate> POUND_FORCE would work just the same if asType()
class and return subtype match, though it would mathematically or
physically make no sense;-)
Am 17.10.2014 04:52 schrieb "Otávio Gonçalves de Santana" <
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And considering the old method, what do avoid me to to something like
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that?:
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Quantity<Time> time = ...;
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Quantity<Length> length = ...;
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Quantity<Mass> result = (Quantity<Mass>) time.multiply(length);
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On Thu, Oct 16, 2014 at 11:28 PM, Otávio Gonçalves de Santana <
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wrote:
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> On Thu, Oct 16, 2014 at 10:03 PM, Martin Desruisseaux <
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> wrote:
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>> Otavio, all the JDK examples you gave below are *safe*, because:
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>>
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>> - In an empty list/set/map, the type of elements (Integer, String,
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>> etc.) become irrelevant.
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>> - In asList, the relationship between input and output types is
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>> correctly expressed. The method signature:
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>> <T> List<T> asList(T... a)
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>> said: "*the type of elements in the list is the same than the type of
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>> the given elements*", which is correct.
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>>
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>> By contract, UNITSOFMEASUREMENT-62 is *unsafe*. The following method
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>> signature:
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>> <T extends Quantity<T>,R extends Quantity<R>> Quantity<R>
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>> multiply(Quantity<T> that)
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>> said: "*there is no relationship between the type of this instance Q,
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>> the input type T and the output type R*" (otherwise, please show me
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>> where the relationship is expressed). The fact that this signature
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>> declares
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>> no relationship is why the compiler accepts anything like "mass =
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>> length.multiply(time)". This method signature is wrong - t*he reality
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>> is not an absence of relationship. The reality is a relationship that we
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>> can not express in Java.*
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>> That is the point, there is two different things the semantic (business
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>> rule) and the Java core source.
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>>
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>> And about the relationship is:
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>> the operations in Quantity results in another quantity.
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>>
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>> So:
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>> Speed = Length.multiply(Time);
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>>
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>> - public interface Speed extends Quantity<Speed>
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>> - public interface Time extends Quantity<Time>
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>> - public interface Speed extends Quantity<Speed>
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>> But I can do same think wrong like this without the implementation take
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>> care:
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>> Mass = Length.multiply(Time);
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>> - Length: Quantity
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>> - Time: Quantity
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>> - Speed: Quantity
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>>
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>>
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>> But it's the first question that I did, take care or not this operations
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>> what it the goals of this JSR.
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>> Martin
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>> Le 17/10/14 08:44, Otávio Gonçalves de Santana a écrit :
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>> About the question of Martin, Yes we can do and there are in in SE api
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>> such java.util.Collections
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>> <http://docs.oracle.com/javase/7/docs/api/java/util/Collections.html>,
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>> java.util.Arrays
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>> <http://docs.oracle.com/javase/7/docs/api/java/util/Arrays.html>, etc.
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>>
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>> List<Integer> intergers = Collections.emptyList();
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>> List<String> strings = Collections.emptyList();
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>>
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>> java.util.Set<Integer> intergersSet = Collections.emptySet();
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>> java.util.Set<String> stringsSet = Collections.emptySet();
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>>
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>> java.util.Map<String, Integer> map = Collections.emptyMap();
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>> java.util.Map<String, String> map2 = Collections.emptyMap();
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>>
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>> List<Long> longs = java.util.Arrays.asList(1L, 2L, 3L);
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>> List<Integer> ints = java.util.Arrays.asList(1, 2, 4);
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>>
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>> I can do something like this and still the Java language :)
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> --
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> Otávio Gonçalves de Santana
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>
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> blog: http://otaviosantana.blogspot.com.br/
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> twitter: http://twitter.com/otaviojava
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> site: *http://about.me/otaviojava <http://about.me/otaviojava>*
>
> 55 (11) 98255-3513
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>
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--
>
Otávio Gonçalves de Santana
>
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blog: http://otaviosantana.blogspot.com.br/
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twitter: http://twitter.com/otaviojava
>
site: *http://about.me/otaviojava <http://about.me/otaviojava>*
>
55 (11) 98255-3513
>
>