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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