Hi Christopher,
I wanted to ask one question concerning your patch,
What's your view on making the EmptyIterator class a proper public class.
Is there a strong reason for deciding that all EmptyIterators must be
the same instance?
It's probably just a style thing, but I wanted to check.
Thanks for the submission,
Bay
On Wed, 21 Nov 2001, Christopher Elkins wrote:
> Hi, all.
>
> Attached are patches to CollectionUtils and its corresponding unit test to
> add support for an "empty" iterator. This is somewhat analogous to JDK2's
> Collections.EMPTY_[LIST|MAP|SET] members.
>
> --
> Christopher Elkins
>
>
> Index: src/java/org/apache/commons/collections/CollectionUtils.java
> ===================================================================
> RCS file:
>/home/cvspublic/jakarta-commons/collections/src/java/org/apache/commons/collections/CollectionUtils.java,v
> retrieving revision 1.5
> diff -u -r1.5 CollectionUtils.java
> --- src/java/org/apache/commons/collections/CollectionUtils.java 2001/08/29
>16:10:29 1.5
> +++ src/java/org/apache/commons/collections/CollectionUtils.java 2001/11/21
>21:41:01
> @@ -80,6 +80,26 @@
> * @version $Id: CollectionUtils.java,v 1.5 2001/08/29 16:10:29 jstrachan Exp $
> */
> public class CollectionUtils {
> +
> + /**
> + * The empty iterator (immutable).
> + */
> + public static final Iterator EMPTY_ITERATOR = new EmptyIterator();
> +
> + private static class EmptyIterator implements Iterator {
> + public boolean hasNext() {
> + return false;
> + }
> +
> + public Object next() {
> + throw new NoSuchElementException();
> + }
> +
> + public void remove() {
> + throw new UnsupportedOperationException();
> + }
> + }
> +
> /**
> * Returns a {@link Collection} containing the union
> * of the given {@link Collection}s.
> Index: src/test/org/apache/commons/collections/TestCollectionUtils.java
> ===================================================================
> RCS file:
>/home/cvspublic/jakarta-commons/collections/src/test/org/apache/commons/collections/TestCollectionUtils.java,v
> retrieving revision 1.2
> diff -u -r1.2 TestCollectionUtils.java
> --- src/test/org/apache/commons/collections/TestCollectionUtils.java 2001/07/14
>23:33:27 1.2
> +++ src/test/org/apache/commons/collections/TestCollectionUtils.java 2001/11/21
>21:41:01
> @@ -310,4 +310,19 @@
> assertTrue(CollectionUtils.isEqualCollection(a,b));
> assertTrue(CollectionUtils.isEqualCollection(b,a));
> }
> +
> + public void testEmptyIterator() {
> + Iterator i = CollectionUtils.EMPTY_ITERATOR;
> + assertTrue(!i.hasNext());
> +
> + try {
> + i.next();
> + fail("Should raise a NoSuchElementException");
> + } catch (NoSuchElementException e) {}
> +
> + try {
> + i.remove();
> + fail("Should raise an UnsupportedOperationException");
> + } catch (UnsupportedOperationException e) {}
> + }
> }
>
> --
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