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Re: for :each style question

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From	Steven Simpson <ss@domain.invalid>
Newsgroups	comp.lang.java.programmer
Subject	Re: for :each style question
Date	Sun, 04 Dec 2011 19:43:18 +0000
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On 30/11/11 23:32, Roedy Green wrote:
> In a for:each loop, sometimes you want to treat the first and or last
> element specially.  [...]
> What do you consider the best style to deal with this?

If I needed it a lot...

import java.util.Arrays;
import java.util.List;

public class FirstLastLoop {
     interface FirstLastBlock<T>  {
         void invoke(T t, boolean isFirst, boolean isLast);
     }

     static<T>  void forEach(Iterable<? extends T>  coll,
                             FirstLastBlock<? super T>  block) {
         boolean isFirst = true;
         boolean lastHeld = false;
         T last = null;
         for (T t : coll) {
             if (lastHeld) {
                 block.invoke(last, isFirst, false);
                 isFirst = false;
             }

             last = t;
             lastHeld = true;
         }
         if (lastHeld)
             block.invoke(last, isFirst, true);
     }

     public static void main(String[] args) throws Exception {
         List<String>  list = Arrays.asList(args);

         FirstLastBlock<String>  block = new FirstLastBlock<String>() {
             public void invoke(String t, boolean isFirst, boolean isLast) {
                 if (isFirst)
                     System.out.print("The list: ");
                 else if (isLast)
                     System.out.print(" and ");
                 else
                     System.out.print(", ");
                 System.out.print(t);
                 if (isLast)
                     System.out.println('.');
             }
         };

         forEach(list, block);

         // Lambda version
         forEach(list, (t, isFirst, isLast) ->  {
                 if (isFirst)
                     System.out.print("The list: ");
                 else if (isLast)
                     System.out.print(" and ");
                 else
                     System.out.print(", ");
                 System.out.print(t);
                 if (isLast)
                     System.out.println('.');
             });
     }
}



-- 
ss at comp dot lancs dot ac dot uk

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for :each style question Roedy Green <see_website@mindprod.com.invalid> - 2011-11-30 15:32 -0800
  Re: for :each style question Arne Vajhøj <arne@vajhoej.dk> - 2011-11-30 19:28 -0500
    Re: for :each style question Chris Riesbeck <Chris.Riesbeck@gmail.com> - 2011-12-05 14:28 -0600
  Re: for :each style question Knute Johnson <nospam@knutejohnson.com> - 2011-11-30 16:49 -0800
    Re: for :each style question Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-11-30 18:23 -0800
      Re: for :each style question Wanja Gayk <brixomatic@yahoo.com> - 2011-12-10 13:28 +0100
        Re: for :each style question Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-12-12 12:07 -0800
          Re: for :each style question Roedy Green <see_website@mindprod.com.invalid> - 2011-12-13 08:08 -0800
            Re: for :each style question Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-12-13 12:07 -0800
          Re: for :each style question Wanja Gayk <brixomatic@yahoo.com> - 2011-12-17 16:20 +0100
        Re: for :each style question Jim Janney <jjanney@shell.xmission.com> - 2011-12-14 14:31 -0700
          Re: for :each style question Lew <lewbloch@gmail.com> - 2011-12-14 16:53 -0800
            Re: for :each style question Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-12-15 16:16 -0800
          Re: for :each style question Wanja Gayk <brixomatic@yahoo.com> - 2011-12-17 12:31 +0100
  Re: for :each style question Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-30 21:35 -0500
  Re: for :each style question Lew <lewbloch@gmail.com> - 2011-11-30 19:12 -0800
  Re: for :each style question Robert Klemme <shortcutter@googlemail.com> - 2011-12-01 23:36 +0100
  Re: for :each style question Steven Simpson <ss@domain.invalid> - 2011-12-04 19:43 +0000

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