Re: Interfaces Question - I am missing something

jmDesktop wrote:


I agree that's a pretty bad example. How about something that Java
actually uses:

public interface Comparable {
   int compareTo( Object o );
}

(Note: typed from memory, and I'm ignoring generics to make the example
simple.)

Here's a simple example. I happen to know that the String class
implements comparable, so I can use that class.

package bubblesort;

public class Main {

     public static void main(String[] args) {
         String[] sortMe = {"B", "Z", "A", "D"};
         sort((Comparable[]) sortMe);
         for (String s : sortMe) {
             System.out.println(s);
         }
     }

     static void sort(Comparable[] list) {
         boolean sorted;
         for (int i = 0; i < list.length - 1; i++)
         {
             sorted = true;
             for (int j = 0; j < list.length - 1 - i; j++)
             {
               if (list[j].compareTo(list[j + 1]) > 0) // The Pay-off
               {
                   Comparable temp = list[j];
                   list[j] = list[j + 1];
                   list[j + 1] = temp;
                   sorted = false;
               }
             }
             if (sorted) {
                 return;
             }
         }
         return;
     }
}

And it sorts anything that implements "Comparable". In this routine,
calling list[j].compareTo() is the same "pay off" that calling wash()
gives you, with a bit more practical application.

Being Washable may not be all that important, but I hope you can see
that Comparable sure is. And future class you define, you can make
Comparable and sort with this one routine (and of course both arrays and
Collections have sorting already, based on Comparable. No need to write
your own at all.)

If not for Comparable, you'd have to write your own sort routine for
each type you create, as Peter says. Now wouldn't that be a pain?