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Java Forum / General / September 2006Doing One Operation on All Array Members (Without Iteration)
I don't think this is possible, but I figure it won't hurt to ask. I just might learn something new. I have an object I've created with a boolean isActive. I can set it my setting the field directly (myObject.isActive = true) or with a setter (myObject.setActive(true)). I will be working with an array, like this: myObject[] Is there any way to do the same operation on all members of that array without using a loop to iterate through each item in the array? In this case, I'd like to set all the members to active at once. It would be like doing: myObject[].setActive(true) I don't think this is possible, but is there a way to do it? Thanks! Hal Hal Vaughan schreef: > I don't think this is possible, but I figure it won't hurt to ask. I just > might learn something new. [quoted text clipped - 13 lines] > > I don't think this is possible, but is there a way to do it? How would you imagine this to work? Suppose, just for a moment, that myObject[].setActive(true) were defined. Then how would it be supposed to work? Unless you have a multi-CPU machine, it will have to go through the array sequentially anyway, so you might as well do the looping yourself, and do null-checking as well in the meantime. H. - -- Hendrik Maryns http://tcl.sfs.uni-tuebingen.de/~hendrik/ ================== http://aouw.org Ask smart questions, get good answers: http://www.catb.org/~esr/faqs/smart-questions.html > Hal Vaughan schreef: >> I don't think this is possible, but I figure it won't hurt to ask. I just [quoted text clipped - 23 lines] > anyway, so you might as well do the looping yourself, and do > null-checking as well in the meantime. Appart from utilizing multiple threads / CPUs to do the job faster is possible, the main point is to remove unnecessary code, thereby making it shorter, simpler, easyer to read and, in final consequence, getting rid of possible hiding places for bugs. Of course, implementing (& using) such a feature could be problematic. For example, having an array containing instances of objects not all of which have a .setActive(boolean) method. OK, an OperationNotSupportedException could be thrown, which means one would have to catch it somewhere and those few lines of code we were trying to get rid of, are here again. So I guess it's down to generics: making sure, that all the entries are suitable. <WishfullThinking> Come to think of it, Mathematica has some powerful features related to such a notion: http://documents.wolfram.com/mathematica/functions/Map (see also Map*, Apply and Operate on the same page). I hear Java is eyeing closures for one its future versions - maybe it could come with Map*, Apply and/or Operate at the same time. </WishfullThinking> > Appart from utilizing multiple threads / CPUs to do the job faster is > possible, Make that _if_ possible. >> Hal Vaughan schreef: >>> I don't think this is possible, but I figure it won't hurt to ask. I [quoted text clipped - 38 lines] > guess it's down to generics: making sure, that all the entries are > suitable. Presumably, myObject has a type, and the operations you could perform on myObject[] would be limited to those defined on the type of myObject. List[] myLists = /*initialize somehow*/ myLists.toString(); /*Calls the method defined on the array*/ myLists[].toString(); /*Calls the method n times, on each element in myList*/ myLists[].add(null); /*This works, as add(Object) is defined in the interface List*/ myLists[].dance(); /*Compile time error, as the interface List doesn't define a method "dance"*/ - Oliver >> Of course, implementing (& using) such a feature could be problematic. >> For example, having an array containing instances of objects not all [quoted text clipped - 17 lines] > myLists[].dance(); /*Compile time error, as the interface List doesn't > define a method "dance"*/ Sure. But consider this. List<Perform> list = ...; Object[] array = list.toArray(); Although Perform could implement .dance(), one couldn't call array.dance(), because Object (and thus Object[]) doesn't. There are many such cases in Java API. Until generics, those seemed reasonable. Now we have a strange mixture. Hi, There is a forAllDo(Collection c, Closure c) in Apache Commons CollectionUtils that might help you, but I am quite positive it ends up iterating the collection anyway..just a little more fancy ;-) http://jakarta.apache.org/commons/collections/apidocs/org/apache/commons/collect ions/CollectionUtils.html -cheers, Manish > I don't think this is possible, but I figure it won't hurt to ask. I just > might learn something new. [quoted text clipped - 17 lines] > > Hal > I don't think this is possible, but I figure it won't hurt to ask. I > just [quoted text clipped - 15 lines] > > I don't think this is possible, but is there a way to do it? What you are probably looking for is something like the functional programming concept of "higher-order functions" (in particular the map function of languages like Haskell and Miranda). Java doesn't really do this (although something similar can be hacked with objects, as it seems to have been in the Jakarta Commons link posted by Manish). Regardless, this just hides the looping from you, something under the covers will still need to make sure that the operation is applied to each element. Joel had an interesting article on first class functions a few weeks ago (http://www.joelonsoftware.com/items/2006/08/01.html). The article on Java that he links to, "Execution in the Kingdom of the Nouns" (http://steve-yegge.blogspot.com/2006/03/execution-in-kingdom-of-nouns.html), is also well worth reading. Dan.  SignatureDaniel Dyer http://www.dandyer.co.uk >myObject[].setActive(true) An approximation would be as follows: interface Operation<Domain>{ void of( Domain value ); } class Thing { public void setActive( final java.lang.Boolean booleanValue ) { java.lang.System.out.println( "setActive." ); }} class Array<T> { final T[] value; Array( final T[] value ){ this.value = value; } public void map( final Operation<T> operation ) { for( final T t : value )operation.of( t ); }} public class Main { static final Array<Thing> things = new Array<Thing> ( new Thing[]{ new Thing(), new Thing(), new Thing() }); public static void main( final java.lang.String[] commandLineArguments ) { things.map( new Operation<Thing>() { public void of( final Thing thing ){ thing.setActive( true ); }}); }} setActive. setActive. setActive. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. 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