On 6 January 2011 12:28, Carl Jokl <[email protected]> wrote:
> It still looks like it may not be possible yet in core Java without
> using google collections or another external library. I suppose the
> desire to be able to do this kind of things would be a driver for
> wanting to add closure to Java.
>
> I get the principle that what I am really doing is mapping one value
> to another value (Remembering Haskell from University) and that order
> does not really matter.
>
> If it were an array of 8 values and a machine had 8 cores then
> potentially the entire operation could be done together. The theory is
> fair enough but I wonder about the overhead of breaking up something
> like this over multiple threads and whether for more trivial
> operations, the overhead of splitting up the computation and doing it
> in parallel might outweigh the time savings of being able to do
> parallel batches. I imagine there is some kind of threshold where the
> parallel processing benefit is greater than the overhead. It may be a
> lower threshold than I realise.
Scala again then, this time from the imminent 2.9 release:
//the .par makes it parallel...
val mnemonics = Type.values.par map { _.getMnemonic }
that'll return a ParArray, suitable for chaining further parallel
operations, but a simple implicit conversion will take it back to a plain
old Java array again if needed (e.g. passing to a function that takes an
array argument)
> On Jan 6, 12:14 pm, Ricky Clarkson <[email protected]> wrote:
> > I think you're looking for map.
> >
> > import fj.F;
> > import fj.data.Array;
> >
> > Integer[] legs = Array(animals).map(new F<Animal, Integer>() {
> > public Integer f(Animal animal) {
> > return animal.legs;
> > }
> >
> > }).array(Integer.class);
> >
> > fj = Functional Java.
> >
> >
> >
> > On Thu, Jan 6, 2011 at 11:47 AM, Carl Jokl <[email protected]> wrote:
> > > One item which I have heard mention recently is that the for loop
> > > syntax is potentially harmful to teach because the for loop with an
> > > index is inherently only processable with a single thread vs the
> > > foreach loop which can potentially use parallel processing.
> >
> > > I use mostly foreach loops but there is one situation in Java where I
> > > seem stuck with using the indexed version. This may be a shortcoming
> > > in Java because the order in which iteration is done does not matter.
> >
> > > The situation is when doing operations which involve copying or
> > > deriving values from one array to another array. The foreach loop in
> > > Java is fine for taking values out of an array but I don't think as
> > > far as I have been able to find out
> > > that these loops can be used for receiving values. In this case the
> > > for loop with the index is used to get an element out of an array at a
> > > given index and the derived value is stored in the destination array
> > > at the same index.
> >
> > > For example:
> >
> > > Type[] types = Type.values();
> > > char[] mnemonics = char[types.length];
> > > for (int index = 0; index < mnemonics.length; index++) {
> > > mnemonics[index] = types[index].getMnemonic();
> > > }
> >
> > > I come across this situation a fair amount but don't think it can be
> > > done in foreach style in Java though I think some kind of closure in
> > > other languages would allow the source to be mapped to the destination
> > > as I understand it.
> >
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