Re: Comparing Collections

["M. Lazarus" <mlazarus@xxxxxxxx>]

James,

 Why not do the test for an unequal number of elements, and execute 
a return, before entering the loop?

 -mark

At 9/2/09 06:53 PM, you wrote:
> Hello All,
> I don't know how often others have to do this, but every once in a while I
> have to compare 2 collections and return an int value like the
> Comparable.compareTo() contract.
>
> Maybe I'm the only one that wants to do this or I'm implementing the objects
> wrong, but I wrote a little utility class to compare 2 collections. Thought
> I would share because there doesn't seem to be much out there.
>
>
> import java.util.ArrayList;
> import java.util.Collection;
> import java.util.List;
>
> /**
>  * @author James R Perkins (JRP)
>  * @version 1.0.0
>  */
> public class CollectionsUtil {
>     private CollectionsUtil() {
>
>     }
>
>     /**
>      * Compares the first collection against the second collection. Returns
> a
>      * negative integer, zero or positive integer.
>      * <p>
>      * If the size of the first collection is greater than the size of the
>      * second collection, a positive integer is return. If the size of the
> first
>      * collection is less than the size of the second collection a negative
>      * number is returned.
>      * </p>
>      *
>      * <p>
>      * If the size of the two collections is equal, then each element from
>      * collection 1 is compared to the element in the same position from
>      * collection 2.
>      * </p>
>      *
>      * @param <T>
>      *            the type of the collection. Both collections must be the
> same
>      *            type and implement {@code java.lang.Comparable}.
>      * @param c1
>      *            the first collection to be compared
>      * @param c2
>      *            the second collection to be compared
>      * @return a negative integer, zero, or a positive integer as the first
>      *         argument is less than, equal to, or greater than the second.
>      */
>     public static <T extends Comparable<? super T>> int compare(
>             Collection<T> c1, Collection<T> c2) {
>         int c = c1.size() - c2.size();
>         List<T> l1 = new ArrayList<T>(c1);
>         List<T> l2 = new ArrayList<T>(c2);
>         for (int i = 0; i < l1.size(); i++) {
>             c = l1.get(i).compareTo(l2.get(i));
>             if (c != 0) {
>                 break;
>             }
>         }
>         return c;
>     }
> }