rework IterableTools and IteratorTools to return more-abstract types

from various methods (typically interfaces instead of concrete classes)

2 files changed, 485 insertions, 175 deletions

diff --git a/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/iterable/IterableTools.java b/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/iterable/IterableTools.java
index 5d0d728da5..0b84ffbed0 100644
--- a/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/iterable/IterableTools.java
+++ b/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/iterable/IterableTools.java
@@ -44,7 +44,7 @@ public final class IterableTools {
 	 * Return a bag corresponding to the specified iterable.

 	 */

 	public static <E> HashBag<E> bag(Iterable<? extends E> iterable) {

-		return CollectionTools.bag(iterable);

+		return IteratorTools.bag(iterable.iterator());

 	}

 

 	/**

@@ -52,14 +52,14 @@ public final class IterableTools {
 	 * The specified iterable size is a performance hint.

 	 */

 	public static <E> HashBag<E> bag(Iterable<? extends E> iterable, int iterableSize) {

-		return CollectionTools.bag(iterable, iterableSize);

+		return IteratorTools.bag(iterable.iterator(), iterableSize);

 	}

 

 	/**

 	 * Return a collection corresponding to the specified iterable.

 	 */

 	public static <E> HashBag<E> collection(Iterable<? extends E> iterable) {

-		return CollectionTools.collection(iterable);

+		return IteratorTools.collection(iterable.iterator());

 	}

 

 	/**

@@ -67,7 +67,7 @@ public final class IterableTools {
 	 * The specified iterable size is a performance hint.

 	 */

 	public static <E> HashBag<E> collection(Iterable<? extends E> iterable, int iterableSize) {

-		return CollectionTools.collection(iterable, iterableSize);

+		return IteratorTools.collection(iterable.iterator(), iterableSize);

 	}

 

 	/**

@@ -349,7 +349,7 @@ public final class IterableTools {
 	 * Return a list corresponding to the specified iterable.

 	 */

 	public static <E> ArrayList<E> list(Iterable<? extends E> iterable) {

-		return ListTools.list(iterable);

+		return IteratorTools.list(iterable.iterator());

 	}

 

 	/**

@@ -357,7 +357,7 @@ public final class IterableTools {
 	 * The specified iterable size is a performance hint.

 	 */

 	public static <E> ArrayList<E> list(Iterable<? extends E> iterable, int iterableSize) {

-		return ListTools.list(iterable, iterableSize);

+		return IteratorTools.list(iterable.iterator(), iterableSize);

 	}

 

 	/**

@@ -386,7 +386,11 @@ public final class IterableTools {
 	 * Return an iterable containing the sorted elements of the specified iterable.

 	 */

 	public static <E> Iterable<E> sort(Iterable<? extends E> iterable, Comparator<? super E> comparator) {

-		return ListTools.sort(ListTools.list(iterable), comparator);

+		Iterator<? extends E> iterator = iterable.iterator();

+		if (iterator.hasNext()) {

+			return ListTools.sort(ListTools.list(iterator), comparator);

+		}

+		return emptyIterable();

 	}

 

 	/**

@@ -394,7 +398,11 @@ public final class IterableTools {
 	 * The specified iterable size is a performance hint.

 	 */

 	public static <E> Iterable<E> sort(Iterable<? extends E> iterable, Comparator<? super E> comparator, int iterableSize) {

-		return ListTools.sort(ListTools.list(iterable, iterableSize), comparator);

+		Iterator<? extends E> iterator = iterable.iterator();

+		if (iterator.hasNext()) {

+			return ListTools.sort(ListTools.list(iterator, iterableSize), comparator);

+		}

+		return emptyIterable();

 	}

 

 	/**

@@ -402,7 +410,7 @@ public final class IterableTools {
 	 * @see Collection#toArray()

 	 */

 	public static Object[] toArray(Iterable<?> iterable) {

-		return list(iterable).toArray();

+		return IteratorTools.toArray(iterable.iterator());

 	}

 

 	/**

@@ -411,7 +419,7 @@ public final class IterableTools {
 	 * @see Collection#toArray()

 	 */

 	public static Object[] toArray(Iterable<?> iterable, int iterableSize) {

-		return list(iterable, iterableSize).toArray();

+		return IteratorTools.toArray(iterable.iterator(), iterableSize);

 	}

 

 	/**

@@ -419,7 +427,7 @@ public final class IterableTools {
 	 * @see Collection#toArray(Object[])

 	 */

 	public static <E> E[] toArray(Iterable<? extends E> iterable, E[] array) {

-		return list(iterable).toArray(array);

+		return IteratorTools.toArray(iterable.iterator(), array);

 	}

 

 	/**

@@ -428,7 +436,7 @@ public final class IterableTools {
 	 * @see Collection#toArray(Object[])

 	 */

 	public static <E> E[] toArray(Iterable<? extends E> iterable, int iterableSize, E[] array) {

-		return list(iterable, iterableSize).toArray(array);

+		return IteratorTools.toArray(iterable.iterator(), iterableSize, array);

 	}

 

 

@@ -439,8 +447,12 @@ public final class IterableTools {
 	 * in the specified iterables.

 	 * @see SimultaneousIterable

 	 */

-	public static <E, I extends Iterable<? extends E>> SimultaneousIterable<E> align(I... iterables) {

-		return align(iterable(iterables), iterables.length);

+	public static <E, I extends Iterable<? extends E>> Iterable<List<E>> align(I... iterables) {

+		int len = iterables.length;

+		if (len == 0) {

+			return emptyIterable();

+		}

+		return align(iterable(iterables), len);

 	}

 

 	/**

@@ -448,8 +460,8 @@ public final class IterableTools {
 	 * in the specified iterables.

 	 * @see SimultaneousIterable

 	 */

-	public static <E, I extends Iterable<? extends E>> SimultaneousIterable<E> align(Iterable<I> iterables) {

-		return new SimultaneousIterable<E>(iterables);

+	public static <E, I extends Iterable<? extends E>> Iterable<List<E>> align(Iterable<I> iterables) {

+		return align(iterables, -1);

 	}

 

 	/**

@@ -457,7 +469,7 @@ public final class IterableTools {
 	 * in the specified iterables.

 	 * @see SimultaneousIterable

 	 */

-	public static <E, I extends Iterable<? extends E>> SimultaneousIterable<E> align(Iterable<I> iterables, int iterablesSize) {

+	public static <E, I extends Iterable<? extends E>> Iterable<List<E>> align(Iterable<I> iterables, int iterablesSize) {

 		return new SimultaneousIterable<E>(iterables, iterablesSize);

 	}

 

@@ -466,8 +478,12 @@ public final class IterableTools {
 	 * in the specified iterables.

 	 * @see SimultaneousListIterable

 	 */

-	public static <E, I extends ListIterable<E>> SimultaneousListIterable<E> alignList(I... iterables) {

-		return alignList(iterable(iterables), iterables.length);

+	public static <E, I extends ListIterable<E>> ListIterable<List<E>> alignList(I... iterables) {

+		int len = iterables.length;

+		if (len == 0) {

+			return emptyListIterable();

+		}

+		return alignList(iterable(iterables), len);

 	}

 

 	/**

@@ -475,8 +491,8 @@ public final class IterableTools {
 	 * in the specified iterables.

 	 * @see SimultaneousListIterable

 	 */

-	public static <E, I extends ListIterable<E>> SimultaneousListIterable<E> alignList(Iterable<I> iterables) {

-		return new SimultaneousListIterable<E>(iterables);

+	public static <E, I extends ListIterable<E>> ListIterable<List<E>> alignList(Iterable<I> iterables) {

+		return alignList(iterables, -1);

 	}

 

 	/**

@@ -484,7 +500,7 @@ public final class IterableTools {
 	 * in the specified iterables.

 	 * @see SimultaneousListIterable

 	 */

-	public static <E, I extends ListIterable<E>> SimultaneousListIterable<E> alignList(Iterable<I> iterables, int iterablesSize) {

+	public static <E, I extends ListIterable<E>> ListIterable<List<E>> alignList(Iterable<I> iterables, int iterablesSize) {

 		return new SimultaneousListIterable<E>(iterables, iterablesSize);

 	}

 

@@ -492,7 +508,7 @@ public final class IterableTools {
 	 * Return an iterable that converts the specified iterable's element type.

 	 * @see LateralIterableWrapper

 	 */

-	public static <E1, E2> LateralIterableWrapper<E1, E2> cast(Iterable<E1> iterable) {

+	public static <E1, E2> Iterable<E2> cast(Iterable<E1> iterable) {

 		return new LateralIterableWrapper<E1, E2>(iterable);

 	}

 

@@ -500,7 +516,7 @@ public final class IterableTools {
 	 * Return a list iterable that converts the specified list iterable's element type.

 	 * @see LateralIterableWrapper

 	 */

-	public static <E1, E2> LateralListIterableWrapper<E1, E2> cast(ListIterable<E1> iterable) {

+	public static <E1, E2> ListIterable<E2> cast(ListIterable<E1> iterable) {

 		return new LateralListIterableWrapper<E1, E2>(iterable);

 	}

 

@@ -508,7 +524,7 @@ public final class IterableTools {
 	 * Return an iterable that converts the specified iterable's element type.

 	 * @see SubIterableWrapper

 	 */

-	public static <E1, E2 extends E1> SubIterableWrapper<E1, E2> downCast(Iterable<E1> iterable) {

+	public static <E1, E2 extends E1> Iterable<E2> downCast(Iterable<E1> iterable) {

 		return new SubIterableWrapper<E1, E2>(iterable);

 	}

 

@@ -516,7 +532,7 @@ public final class IterableTools {
 	 * Return an iterable that converts the specified iterable's element type.

 	 * @see SubListIterableWrapper

 	 */

-	public static <E1, E2 extends E1> SubListIterableWrapper<E1, E2> downCast(ListIterable<E1> iterable) {

+	public static <E1, E2 extends E1> ListIterable<E2> downCast(ListIterable<E1> iterable) {

 		return new SubListIterableWrapper<E1, E2>(iterable);

 	}

 

@@ -524,7 +540,7 @@ public final class IterableTools {
 	 * Return an iterable that converts the specified iterable's element type.

 	 * @see SuperIterableWrapper

 	 */

-	public static <E> SuperIterableWrapper<E> upCast(Iterable<? extends E> iterable) {

+	public static <E> Iterable<E> upCast(Iterable<? extends E> iterable) {

 		return new SuperIterableWrapper<E>(iterable);

 	}

 

@@ -532,7 +548,7 @@ public final class IterableTools {
 	 * Return an iterable that converts the specified iterable's element type.

 	 * @see SuperListIterableWrapper

 	 */

-	public static <E> SuperListIterableWrapper<E> upCast(ListIterable<? extends E> iterable) {

+	public static <E> ListIterable<E> upCast(ListIterable<? extends E> iterable) {

 		return new SuperListIterableWrapper<E>(iterable);

 	}

 

@@ -541,7 +557,10 @@ public final class IterableTools {
 	 * the specified {@link Transformer transformer}.

 	 * @see ChainIterable

 	 */

-	public static <E> ChainIterable<E> chainIterable(E first, Transformer<? super E, ? extends E> transformer) {

+	public static <E> Iterable<E> chainIterable(E first, Transformer<? super E, ? extends E> transformer) {

+		if (first == null) {

+			return emptyIterable();

+		}

 		return new ChainIterable<E>(first, transformer);

 	}

 

@@ -550,7 +569,7 @@ public final class IterableTools {
 	 * elements.

 	 * @see LiveCloneIterable

 	 */

-	public static <E> LiveCloneIterable<E> cloneLive(Collection<? extends E> collection) {

+	public static <E> Iterable<E> cloneLive(Collection<? extends E> collection) {

 		return cloneLive(collection, DisabledClosure.instance());

 	}

 

@@ -559,7 +578,7 @@ public final class IterableTools {
 	 * elements and uses the specified remove closure.

 	 * @see LiveCloneIterable

 	 */

-	public static <E> LiveCloneIterable<E> cloneLive(Collection<? extends E> collection, Closure<? super E> removeClosure) {

+	public static <E> Iterable<E> cloneLive(Collection<? extends E> collection, Closure<? super E> removeClosure) {

 		return new LiveCloneIterable<E>(collection, removeClosure);

 	}

 

@@ -568,7 +587,7 @@ public final class IterableTools {
 	 * elements.

 	 * @see LiveCloneListIterable

 	 */

-	public static <E> LiveCloneListIterable<E> cloneLive(List<? extends E> list) {

+	public static <E> ListIterable<E> cloneLive(List<? extends E> list) {

 		return cloneLive(list, CloneListIterator.Adapter.ReadOnly.<E>instance());

 	}

 

@@ -577,7 +596,7 @@ public final class IterableTools {
 	 * elements and uses the specified {@link org.eclipse.jpt.common.utility.internal.iterator.CloneListIterator.Adapter adapter}.

 	 * @see LiveCloneListIterable

 	 */

-	public static <E> LiveCloneListIterable<E> cloneLive(List<? extends E> list, CloneListIterator.Adapter<E> adapter) {

+	public static <E> ListIterable<E> cloneLive(List<? extends E> list, CloneListIterator.Adapter<E> adapter) {

 		return new LiveCloneListIterable<E>(list, adapter);

 	}

 

@@ -586,16 +605,19 @@ public final class IterableTools {
 	 * elements.

 	 * @see SnapshotCloneIterable

 	 */

-	public static <E> SnapshotCloneIterable<E> cloneSnapshot(Collection<? extends E> collection) {

+	public static <E> Iterable<E> cloneSnapshot(Collection<? extends E> collection) {

 		return cloneSnapshot(collection, DisabledClosure.instance());

 	}

 

 	/**

 	 * Return an iterable that clones the specified collection before returning

 	 * elements and uses the specified remove closure.

-	 * @see LiveCloneIterable

+	 * @see SnapshotCloneIterable

 	 */

-	public static <E> SnapshotCloneIterable<E> cloneSnapshot(Collection<? extends E> collection, Closure<? super E> removeClosure) {

+	public static <E> Iterable<E> cloneSnapshot(Collection<? extends E> collection, Closure<? super E> removeClosure) {

+		if (collection.isEmpty()) {

+			return emptyIterable();

+		}

 		return new SnapshotCloneIterable<E>(collection, removeClosure);

 	}

 

@@ -604,7 +626,7 @@ public final class IterableTools {
 	 * elements.

 	 * @see SnapshotCloneListIterable

 	 */

-	public static <E> SnapshotCloneListIterable<E> cloneSnapshot(List<? extends E> list) {

+	public static <E> ListIterable<E> cloneSnapshot(List<? extends E> list) {

 		return cloneSnapshot(list, CloneListIterator.Adapter.ReadOnly.<E>instance());

 	}

 

@@ -613,7 +635,10 @@ public final class IterableTools {
 	 * elements and uses the specified {@link org.eclipse.jpt.common.utility.internal.iterator.CloneListIterator.Adapter adapter}.

 	 * @see SnapshotCloneListIterable

 	 */

-	public static <E> SnapshotCloneListIterable<E> cloneSnapshot(List<? extends E> list, CloneListIterator.Adapter<E> adapter) {

+	public static <E> ListIterable<E> cloneSnapshot(List<? extends E> list, CloneListIterator.Adapter<E> adapter) {

+		if (list.isEmpty()) {

+			return emptyListIterable();

+		}

 		return new SnapshotCloneListIterable<E>(list, adapter);

 	}

 

@@ -623,8 +648,8 @@ public final class IterableTools {
 	 * @see CompositeIterable

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> CompositeIterable<E> add(Iterable<? extends E> iterable, E object) {

-		return concatenate(iterable, singletonIterable(object));

+	public static <E> Iterable<E> add(Iterable<? extends E> iterable, E object) {

+		return concatenate_(iterable, singletonIterable(object));

 	}

 

 	/**

@@ -633,8 +658,8 @@ public final class IterableTools {
 	 * @see CompositeIterable

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> CompositeIterable<E> insert(E object, Iterable<? extends E> iterable) {

-		return concatenate(singletonIterable(object), iterable);

+	public static <E> Iterable<E> insert(E object, Iterable<? extends E> iterable) {

+		return concatenate_(singletonIterable(object), iterable);

 	}

 

 	/**

@@ -642,7 +667,22 @@ public final class IterableTools {
 	 * elements in the specified iterables.

 	 * @see CompositeIterable

 	 */

-	public static <E> CompositeIterable<E> concatenate(Iterable<? extends E>... iterables) {

+	@SuppressWarnings("unchecked")

+	public static <E> Iterable<E> concatenate(Iterable<? extends E>... iterables) {

+		int len = iterables.length;

+		if (len == 0) {

+			return emptyIterable();

+		}

+		if (len == 1) {

+			return (Iterable<E>) iterables[0];

+		}

+		return concatenate_(iterables);

+	}

+

+	/**

+	 * assume the list is not empty

+	 */

+	private static <E> Iterable<E> concatenate_(Iterable<? extends E>... iterables) {

 		return concatenate(Arrays.asList(iterables));

 	}

 

@@ -651,7 +691,7 @@ public final class IterableTools {
 	 * elements in the specified iterables.

 	 * @see CompositeIterable

 	 */

-	public static <E> CompositeIterable<E> concatenate(Iterable<? extends Iterable<? extends E>> iterables) {

+	public static <E> Iterable<E> concatenate(Iterable<? extends Iterable<? extends E>> iterables) {

 		return new CompositeIterable<E>(iterables);

 	}

 

@@ -660,7 +700,7 @@ public final class IterableTools {
 	 * Use the specified transformer to transform each parent into its children.

 	 * @see CompositeIterable

 	 */

-	public static <P, E> CompositeIterable<E> children(Iterable<? extends P> parents, Transformer<? super P, ? extends Iterable<? extends E>> childrenTransformer) {

+	public static <P, E> Iterable<E> children(Iterable<? extends P> parents, Transformer<? super P, ? extends Iterable<? extends E>> childrenTransformer) {

 		return concatenate(transform(parents, childrenTransformer));

 	}

 

@@ -670,8 +710,8 @@ public final class IterableTools {
 	 * @see CompositeListIterable

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> CompositeListIterable<E> add(ListIterable<E> iterable, E object) {

-		return concatenate(iterable, singletonListIterable(object));

+	public static <E> ListIterable<E> add(ListIterable<E> iterable, E object) {

+		return concatenate_(iterable, singletonListIterable(object));

 	}

 

 	/**

@@ -680,8 +720,8 @@ public final class IterableTools {
 	 * @see CompositeListIterable

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> CompositeListIterable<E> insert(E object, ListIterable<E> iterable) {

-		return concatenate(singletonListIterable(object), iterable);

+	public static <E> ListIterable<E> insert(E object, ListIterable<E> iterable) {

+		return concatenate_(singletonListIterable(object), iterable);

 	}

 

 	/**

@@ -689,7 +729,21 @@ public final class IterableTools {
 	 * elements in the specified iterables.

 	 * @see CompositeListIterable

 	 */

-	public static <E> CompositeListIterable<E> concatenate(ListIterable<E>... iterables) {

+	public static <E> ListIterable<E> concatenate(ListIterable<E>... iterables) {

+		int len = iterables.length;

+		if (len == 0) {

+			return emptyListIterable();

+		}

+		if (len == 1) {

+			return iterables[0];

+		}

+		return concatenate_(iterables);

+	}

+

+	/**

+	 * assume the list is not empty

+	 */

+	private static <E> ListIterable<E> concatenate_(ListIterable<E>... iterables) {

 		return concatenate(listIterable(iterables));

 	}

 

@@ -698,7 +752,7 @@ public final class IterableTools {
 	 * elements in the specified iterables.

 	 * @see CompositeListIterable

 	 */

-	public static <E> CompositeListIterable<E> concatenate(ListIterable<? extends ListIterable<E>> iterables) {

+	public static <E> ListIterable<E> concatenate(ListIterable<? extends ListIterable<E>> iterables) {

 		return new CompositeListIterable<E>(iterables);

 	}

 

@@ -707,7 +761,7 @@ public final class IterableTools {
 	 * Use the specified transformer to transform each parent into its children.

 	 * @see CompositeListIterable

 	 */

-	public static <P, E> CompositeListIterable<E> children(ListIterable<? extends P> parents, Transformer<? super P, ? extends ListIterable<E>> childrenTransformer) {

+	public static <P, E> ListIterable<E> children(ListIterable<? extends P> parents, Transformer<? super P, ? extends ListIterable<E>> childrenTransformer) {

 		return concatenate(transform(parents, childrenTransformer));

 	}

 

@@ -717,8 +771,8 @@ public final class IterableTools {
 	 * @see ReadOnlyCompositeListIterable

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> ReadOnlyCompositeListIterable<E> addReadOnly(ListIterable<? extends E> iterable, E object) {

-		return concatenateReadOnly(iterable, singletonListIterable(object));

+	public static <E> ListIterable<E> addReadOnly(ListIterable<? extends E> iterable, E object) {

+		return concatenateReadOnly_(iterable, singletonListIterable(object));

 	}

 

 	/**

@@ -727,8 +781,8 @@ public final class IterableTools {
 	 * @see ReadOnlyCompositeListIterable

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> ReadOnlyCompositeListIterable<E> insertReadOnly(E object, ListIterable<? extends E> iterable) {

-		return concatenateReadOnly(singletonListIterable(object), iterable);

+	public static <E> ListIterable<E> insertReadOnly(E object, ListIterable<? extends E> iterable) {

+		return concatenateReadOnly_(singletonListIterable(object), iterable);

 	}

 

 	/**

@@ -736,7 +790,22 @@ public final class IterableTools {
 	 * elements in the specified iterables.

 	 * @see ReadOnlyCompositeListIterable

 	 */

-	public static <E> ReadOnlyCompositeListIterable<E> concatenateReadOnly(ListIterable<? extends E>... iterables) {

+	@SuppressWarnings("unchecked")

+	public static <E> ListIterable<E> concatenateReadOnly(ListIterable<? extends E>... iterables) {

+		int len = iterables.length;

+		if (len == 0) {

+			return emptyListIterable();

+		}

+		if (len == 1) {

+			return (ListIterable<E>) iterables[0];

+		}

+		return concatenateReadOnly_(iterables);

+	}

+

+	/**

+	 * assume the list is not empty

+	 */

+	private static <E> ListIterable<E> concatenateReadOnly_(ListIterable<? extends E>... iterables) {

 		return concatenateReadOnly(listIterable(iterables));

 	}

 

@@ -745,7 +814,7 @@ public final class IterableTools {
 	 * elements in the specified iterables.

 	 * @see ReadOnlyCompositeListIterable

 	 */

-	public static <E> ReadOnlyCompositeListIterable<E> concatenateReadOnly(ListIterable<? extends ListIterable<? extends E>> iterables) {

+	public static <E> ListIterable<E> concatenateReadOnly(ListIterable<? extends ListIterable<? extends E>> iterables) {

 		return new ReadOnlyCompositeListIterable<E>(iterables);

 	}

 

@@ -754,7 +823,7 @@ public final class IterableTools {
 	 * Use the specified transformer to transform each parent into its children.

 	 * @see ReadOnlyCompositeListIterable

 	 */

-	public static <P, E> ReadOnlyCompositeListIterable<E> readOnlyChildren(ListIterable<? extends P> parents, Transformer<? super P, ? extends ListIterable<? extends E>> childrenTransformer) {

+	public static <P, E> ListIterable<E> readOnlyChildren(ListIterable<? extends P> parents, Transformer<? super P, ? extends ListIterable<? extends E>> childrenTransformer) {

 		return concatenateReadOnly(transform(parents, childrenTransformer));

 	}

 

@@ -777,7 +846,7 @@ public final class IterableTools {
 	 * elements in the specified iterable.

 	 * @see FilteringIterable

 	 */

-	public static <E> FilteringIterable<E> filter(Iterable<? extends E> iterable, Predicate<? super E> predicate) {

+	public static <E> Iterable<E> filter(Iterable<? extends E> iterable, Predicate<? super E> predicate) {

 		return new FilteringIterable<E>(iterable, predicate);

 	}

 

@@ -786,7 +855,7 @@ public final class IterableTools {
 	 * elements in the specified iterable.

 	 * @see FilteringIterable

 	 */

-	public static <E> FilteringIterable<E> removeNulls(Iterable<? extends E> iterable) {

+	public static <E> Iterable<E> removeNulls(Iterable<? extends E> iterable) {

 		return filter(iterable, PredicateTools.isNotNull());

 	}

 

@@ -795,7 +864,7 @@ public final class IterableTools {
 	 * by its children etc. as determined by the specified transformer.

 	 * @see GraphIterable

 	 */

-	public static <E> GraphIterable<E> graphIterable(E root, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

+	public static <E> Iterable<E> graphIterable(E root, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

 		return graphIterable(singletonIterable(root), transformer);

 	}

 

@@ -804,7 +873,10 @@ public final class IterableTools {
 	 * by their children etc. as determined by the specified transformer.

 	 * @see GraphIterable

 	 */

-	public static <E> GraphIterable<E> graphIterable(E[] roots, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

+	public static <E> Iterable<E> graphIterable(E[] roots, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

+		if (roots.length == 0) {

+			return emptyIterable();

+		}

 		return graphIterable(Arrays.asList(roots), transformer);

 	}

 

@@ -813,14 +885,14 @@ public final class IterableTools {
 	 * by their children etc. as determined by the specified transformer.

 	 * @see GraphIterable

 	 */

-	public static <E> GraphIterable<E> graphIterable(Iterable<? extends E> roots, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

+	public static <E> Iterable<E> graphIterable(Iterable<? extends E> roots, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

 		return new GraphIterable<E>(roots, transformer);

 	}

 

 	/**

 	 * Return an iterable on the elements in the specified array.

 	 */

-	public static <E> ArrayIterable<E> iterable(E... array) {

+	public static <E> Iterable<E> iterable(E... array) {

 		return iterable(array, 0);

 	}

 

@@ -828,7 +900,7 @@ public final class IterableTools {
 	 * Return an iterable on the elements in the specified array

 	 * starting at the specified position in the array.

 	 */

-	public static <E> ArrayIterable<E> iterable(E[] array, int start) {

+	public static <E> Iterable<E> iterable(E[] array, int start) {

 		return iterable(array, start, array.length);

 	}

 

@@ -837,7 +909,10 @@ public final class IterableTools {
 	 * starting at the specified start index, inclusive, and continuing to

 	 * the specified end index, exclusive.

 	 */

-	public static <E> ArrayIterable<E> iterable(E[] array, int start, int end) {

+	public static <E> Iterable<E> iterable(E[] array, int start, int end) {

+		if (start == end) {

+			return emptyIterable();

+		}

 		return new ArrayIterable<E>(array, start, end);

 	}

 

@@ -845,7 +920,7 @@ public final class IterableTools {
 	 * Return an iterable on the specified queue.

 	 * @see Queue

 	 */

-	public static <E> QueueIterable<E> iterable(Queue<? extends E> queue) {

+	public static <E> Iterable<E> iterable(Queue<? extends E> queue) {

 		return new QueueIterable<E>(queue);

 	}

 

@@ -853,14 +928,14 @@ public final class IterableTools {
 	 * Return an iterable on the specified stack.

 	 * @see Stack

 	 */

-	public static <E> StackIterable<E> iterable(Stack<? extends E> stack) {

+	public static <E> Iterable<E> iterable(Stack<? extends E> stack) {

 		return new StackIterable<E>(stack);

 	}

 

 	/**

 	 * Return a list iterable for the specified array.

 	 */

-	public static <E> ArrayListIterable<E> listIterable(E... array) {

+	public static <E> ListIterable<E> listIterable(E... array) {

 		return listIterable(array, 0);

 	}

 

@@ -868,7 +943,7 @@ public final class IterableTools {
 	 * Return a list iterable for the specified array

 	 * starting at the specified position in the array.

 	 */

-	public static <E> ArrayListIterable<E> listIterable(E[] array, int start) {

+	public static <E> ListIterable<E> listIterable(E[] array, int start) {

 		return listIterable(array, start, array.length);

 	}

 

@@ -877,14 +952,17 @@ public final class IterableTools {
 	 * starting at the specified start index, inclusive, and continuing to

 	 * the specified end index, exclusive.

 	 */

-	public static <E> ArrayListIterable<E> listIterable(E[] array, int start, int end) {

+	public static <E> ListIterable<E> listIterable(E[] array, int start, int end) {

+		if (start == end) {

+			return emptyListIterable();

+		}

 		return new ArrayListIterable<E>(array, start, end);

 	}

 

 	/**

 	 * Return a list iterable for the specified list.

 	 */

-	public static <E> ListListIterable<E> listIterable(List<E> list) {

+	public static <E> ListIterable<E> listIterable(List<E> list) {

 		return new ListListIterable<E>(list);

 	}

 

@@ -901,7 +979,7 @@ public final class IterableTools {
 	 * Convert the specified iterable to read-only.

 	 * @see ReadOnlyIterable

 	 */

-	public static <E> ReadOnlyIterable<E> readOnly(Iterable<? extends E> iterable) {

+	public static <E> Iterable<E> readOnly(Iterable<? extends E> iterable) {

 		return new ReadOnlyIterable<E>(iterable);

 	}

 

@@ -909,7 +987,7 @@ public final class IterableTools {
 	 * Convert the specified iterable to read-only.

 	 * @see ReadOnlyListIterable

 	 */

-	public static <E> ReadOnlyListIterable<E> readOnly(ListIterable<? extends E> iterable) {

+	public static <E> ListIterable<E> readOnly(ListIterable<? extends E> iterable) {

 		return new ReadOnlyListIterable<E>(iterable);

 	}

 

@@ -918,7 +996,7 @@ public final class IterableTools {
 	 * specified object.

 	 * @see SingleElementIterable

 	 */

-	public static <E> SingleElementIterable<E> singletonIterable(E value) {

+	public static <E> Iterable<E> singletonIterable(E value) {

 		return new SingleElementIterable<E>(value);

 	}

 

@@ -927,7 +1005,7 @@ public final class IterableTools {
 	 * specified object.

 	 * @see SingleElementListIterable

 	 */

-	public static <E> SingleElementListIterable<E> singletonListIterable(E value) {

+	public static <E> ListIterable<E> singletonListIterable(E value) {

 		return new SingleElementListIterable<E>(value);

 	}

 

@@ -936,7 +1014,7 @@ public final class IterableTools {
 	 * elements in the specified iterable.

 	 * @see TransformationIterable

 	 */

-	public static <E1, E2> TransformationIterable<E1, E2> transform(Iterable<? extends E1> iterable, Transformer<? super E1, ? extends E2> transformer) {

+	public static <E1, E2> Iterable<E2> transform(Iterable<? extends E1> iterable, Transformer<? super E1, ? extends E2> transformer) {

 		return new TransformationIterable<E1, E2>(iterable, transformer);

 	}

 

@@ -945,7 +1023,7 @@ public final class IterableTools {
 	 * elements in the specified iterable.

 	 * @see TransformationListIterable

 	 */

-	public static <E1, E2, T extends E1> TransformationListIterable<E1, E2> transform(ListIterable<T> iterable, Transformer<? super E1, ? extends E2> transformer) {

+	public static <E1, E2, T extends E1> ListIterable<E2> transform(ListIterable<T> iterable, Transformer<? super E1, ? extends E2> transformer) {

 		return new TransformationListIterable<E1, E2>(iterable, transformer);

 	}

 

@@ -954,7 +1032,7 @@ public final class IterableTools {
 	 * with the specified root and transformer.

 	 * @see TreeIterable

 	 */

-	public static <E> TreeIterable<E> treeIterable(E root, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

+	public static <E> Iterable<E> treeIterable(E root, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

 		return treeIterable(singletonIterable(root), transformer);

 	}

 

@@ -963,7 +1041,10 @@ public final class IterableTools {
 	 * with the specified roots and transformer.

 	 * @see TreeIterable

 	 */

-	public static <E> TreeIterable<E> treeIterable(E[] roots, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

+	public static <E> Iterable<E> treeIterable(E[] roots, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

+		if (roots.length == 0) {

+			return emptyIterable();

+		}

 		return treeIterable(iterable(roots), transformer);

 	}

 

@@ -972,7 +1053,7 @@ public final class IterableTools {
 	 * with the specified roots and transformer.

 	 * @see TreeIterable

 	 */

-	public static <E> TreeIterable<E> treeIterable(Iterable<? extends E> roots, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

+	public static <E> Iterable<E> treeIterable(Iterable<? extends E> roots, Transformer<? super E, ? extends Iterable<? extends E>> transformer) {

 		return new TreeIterable<E>(roots, transformer);

 	}

 

diff --git a/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/iterator/IteratorTools.java b/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/iterator/IteratorTools.java
index 3c95c00258..2dc251b80d 100644
--- a/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/iterator/IteratorTools.java
+++ b/common/plugins/org.eclipse.jpt.common.utility/src/org/eclipse/jpt/common/utility/internal/iterator/IteratorTools.java
@@ -21,11 +21,13 @@ import org.eclipse.jpt.common.utility.closure.InterruptibleClosure;
 import org.eclipse.jpt.common.utility.collection.Queue;

 import org.eclipse.jpt.common.utility.collection.Stack;

 import org.eclipse.jpt.common.utility.exception.ExceptionHandler;

+import org.eclipse.jpt.common.utility.internal.ArrayTools;

 import org.eclipse.jpt.common.utility.internal.ObjectTools;

 import org.eclipse.jpt.common.utility.internal.closure.DisabledClosure;

 import org.eclipse.jpt.common.utility.internal.collection.CollectionTools;

 import org.eclipse.jpt.common.utility.internal.collection.HashBag;

 import org.eclipse.jpt.common.utility.internal.collection.ListTools;

+import org.eclipse.jpt.common.utility.internal.enumeration.EnumerationTools;

 import org.eclipse.jpt.common.utility.internal.iterable.IterableTools;

 import org.eclipse.jpt.common.utility.internal.iterator.CloneListIterator.Adapter;

 import org.eclipse.jpt.common.utility.internal.predicate.PredicateTools;

@@ -153,7 +155,7 @@ public final class IteratorTools {
 	 * elements in the specified collection.

 	 */

 	public static boolean containsAll(Iterator<?> iterator, Collection<?> collection) {

-		return CollectionTools.set(iterator).containsAll(collection);

+		return collection.isEmpty() || CollectionTools.set(iterator).containsAll(collection);

 	}

 

 	/**

@@ -162,7 +164,7 @@ public final class IteratorTools {
 	 * The specified iterator size is a performance hint.

 	 */

 	public static boolean containsAll(Iterator<?> iterator, int iteratorSize, Collection<?> collection) {

-		return CollectionTools.set(iterator, iteratorSize).containsAll(collection);

+		return collection.isEmpty() || CollectionTools.set(iterator, iteratorSize).containsAll(collection);

 	}

 

 	/**

@@ -170,7 +172,7 @@ public final class IteratorTools {
 	 * elements in the specified iterable.

 	 */

 	public static boolean containsAll(Iterator<?> iterator, Iterable<?> iterable) {

-		return CollectionTools.containsAll(CollectionTools.set(iterator), iterable);

+		return containsAll(iterator, iterable.iterator());

 	}

 

 	/**

@@ -179,7 +181,7 @@ public final class IteratorTools {
 	 * The specified iterator size is a performance hint.

 	 */

 	public static boolean containsAll(Iterator<?> iterator, int iteratorSize, Iterable<?> iterable) {

-		return CollectionTools.containsAll(CollectionTools.set(iterator, iteratorSize), iterable);

+		return containsAll(iterator, iteratorSize, iterable.iterator());

 	}

 

 	/**

@@ -187,7 +189,7 @@ public final class IteratorTools {
 	 * elements in the specified iterator 2.

 	 */

 	public static boolean containsAll(Iterator<?> iterator1, Iterator<?> iterator2) {

-		return CollectionTools.containsAll(CollectionTools.set(iterator1), iterator2);

+		return isEmpty(iterator2) || CollectionTools.containsAll(CollectionTools.set(iterator1), iterator2);

 	}

 

 	/**

@@ -196,7 +198,7 @@ public final class IteratorTools {
 	 * The specified iterator 1 size is a performance hint.

 	 */

 	public static boolean containsAll(Iterator<?> iterator1, int iterator1Size, Iterator<?> iterator2) {

-		return CollectionTools.containsAll(CollectionTools.set(iterator1, iterator1Size), iterator2);

+		return isEmpty(iterator2) || CollectionTools.containsAll(CollectionTools.set(iterator1, iterator1Size), iterator2);

 	}

 

 	/**

@@ -204,7 +206,7 @@ public final class IteratorTools {
 	 * elements in the specified array.

 	 */

 	public static boolean containsAll(Iterator<?> iterator, Object... array) {

-		return CollectionTools.containsAll(CollectionTools.set(iterator), array);

+		return (array.length == 0) || CollectionTools.containsAll(CollectionTools.set(iterator), array);

 	}

 

 	/**

@@ -213,7 +215,7 @@ public final class IteratorTools {
 	 * The specified iterator size is a performance hint.

 	 */

 	public static boolean containsAll(Iterator<?> iterator, int iteratorSize, Object... array) {

-		return CollectionTools.containsAll(CollectionTools.set(iterator, iteratorSize), array);

+		return (array.length == 0) || CollectionTools.containsAll(CollectionTools.set(iterator, iteratorSize), array);

 	}

 

 	/**

@@ -318,9 +320,10 @@ public final class IteratorTools {
 		int i = 0;

 		while (iterator.hasNext()) {

 			E next = iterator.next();

-			if (i++ == index) {

+			if (i == index) {

 				return next;

 			}

+			i++;

 		}

 		throw new IndexOutOfBoundsException(String.valueOf(index) + ':' + String.valueOf(i));

 	}

@@ -527,6 +530,9 @@ public final class IteratorTools {
 	 * Return the iterator after it has been "sorted".

 	 */

 	public static <E> ListIterator<E> sort(Iterator<? extends E> iterator, Comparator<? super E> comparator) {

+		if (isEmpty(iterator)) {

+			return emptyListIterator();

+		}

 		return ListTools.sort(ListTools.list(iterator), comparator).listIterator();

 	}

 

@@ -535,6 +541,9 @@ public final class IteratorTools {
 	 * The specified iterator size is a performance hint.

 	 */

 	public static <E> ListIterator<E> sort(Iterator<? extends E> iterator, Comparator<? super E> comparator, int iteratorSize) {

+		if (isEmpty(iterator)) {

+			return emptyListIterator();

+		}

 		return ListTools.sort(ListTools.list(iterator, iteratorSize), comparator).listIterator();

 	}

 

@@ -543,7 +552,7 @@ public final class IteratorTools {
 	 * @see Collection#toArray()

 	 */

 	public static Object[] toArray(Iterator<?> iterator) {

-		return list(iterator).toArray();

+		return isEmpty(iterator) ? ObjectTools.EMPTY_OBJECT_ARRAY : list(iterator).toArray();

 	}

 

 	/**

@@ -552,7 +561,7 @@ public final class IteratorTools {
 	 * @see Collection#toArray()

 	 */

 	public static Object[] toArray(Iterator<?> iterator, int iteratorSize) {

-		return list(iterator, iteratorSize).toArray();

+		return isEmpty(iterator) ? ObjectTools.EMPTY_OBJECT_ARRAY : list(iterator, iteratorSize).toArray();

 	}

 

 	/**

@@ -560,7 +569,7 @@ public final class IteratorTools {
 	 * @see Collection#toArray(Object[])

 	 */

 	public static <E> E[] toArray(Iterator<? extends E> iterator, E[] array) {

-		return list(iterator).toArray(array);

+		return isEmpty(iterator) ? ArrayTools.newInstance(array, 0) : list(iterator).toArray(array);

 	}

 

 	/**

@@ -569,7 +578,7 @@ public final class IteratorTools {
 	 * @see Collection#toArray(Object[])

 	 */

 	public static <E> E[] toArray(Iterator<? extends E> iterator, int iteratorSize, E[] array) {

-		return list(iterator, iteratorSize).toArray(array);

+		return isEmpty(iterator) ? ArrayTools.newInstance(array, 0) : list(iterator, iteratorSize).toArray(array);

 	}

 

 

@@ -580,8 +589,12 @@ public final class IteratorTools {
 	 * in the specified iterators.

 	 * @see SimultaneousIterator

 	 */

-	public static <E, I extends Iterator<? extends E>> SimultaneousIterator<E> align(I... iterators) {

-		return align(IterableTools.iterable(iterators), iterators.length);

+	public static <E, I extends Iterator<? extends E>> Iterator<List<E>> align(I... iterators) {

+		int len = iterators.length;

+		if (len == 0) {

+			return emptyIterator();

+		}

+		return align(IterableTools.iterable(iterators), len);

 	}

 

 	/**

@@ -589,8 +602,8 @@ public final class IteratorTools {
 	 * in the specified iterables.

 	 * @see SimultaneousIterator

 	 */

-	public static <E, I extends Iterator<? extends E>> SimultaneousIterator<E> align(Iterable<I> iterables) {

-		return new SimultaneousIterator<E>(iterables);

+	public static <E, I extends Iterator<? extends E>> Iterator<List<E>> align(Iterable<I> iterables) {

+		return align(iterables, -1);

 	}

 

 	/**

@@ -598,7 +611,7 @@ public final class IteratorTools {
 	 * in the specified iterables.

 	 * @see SimultaneousIterator

 	 */

-	public static <E, I extends Iterator<? extends E>> SimultaneousIterator<E> align(Iterable<I> iterables, int iterablesSize) {

+	public static <E, I extends Iterator<? extends E>> Iterator<List<E>> align(Iterable<I> iterables, int iterablesSize) {

 		return new SimultaneousIterator<E>(iterables, iterablesSize);

 	}

 

@@ -607,8 +620,12 @@ public final class IteratorTools {
 	 * in the specified iterators.

 	 * @see SimultaneousListIterator

 	 */

-	public static <E, I extends ListIterator<E>> SimultaneousListIterator<E> alignList(I... iterators) {

-		return alignList(IterableTools.listIterable(iterators), iterators.length);

+	public static <E, I extends ListIterator<E>> ListIterator<List<E>> alignList(I... iterators) {

+		int len = iterators.length;

+		if (len == 0) {

+			return emptyListIterator();

+		}

+		return alignList(IterableTools.listIterable(iterators), len);

 	}

 

 	/**

@@ -616,8 +633,8 @@ public final class IteratorTools {
 	 * in the specified iterables.

 	 * @see SimultaneousListIterator

 	 */

-	public static <E, I extends ListIterator<E>> SimultaneousListIterator<E> alignList(Iterable<I> iterables) {

-		return new SimultaneousListIterator<E>(iterables);

+	public static <E, I extends ListIterator<E>> ListIterator<List<E>> alignList(Iterable<I> iterables) {

+		return alignList(iterables, -1);

 	}

 

 	/**

@@ -625,7 +642,7 @@ public final class IteratorTools {
 	 * in the specified iterators.

 	 * @see SimultaneousListIterator

 	 */

-	public static <E, I extends ListIterator<E>> SimultaneousListIterator<E> alignList(Iterable<I> iterators, int iteratorsSize) {

+	public static <E, I extends ListIterator<E>> ListIterator<List<E>> alignList(Iterable<I> iterators, int iteratorsSize) {

 		return new SimultaneousListIterator<E>(iterators, iteratorsSize);

 	}

 

@@ -633,7 +650,10 @@ public final class IteratorTools {
 	 * Return an iterator that converts the specified iterator's element type.

 	 * @see LateralIteratorWrapper

 	 */

-	public static <E1, E2> LateralIteratorWrapper<E1, E2> cast(Iterator<E1> iterator) {

+	public static <E1, E2> Iterator<E2> cast(Iterator<E1> iterator) {

+		if (isEmpty(iterator)) {

+			return emptyIterator();

+		}

 		return new LateralIteratorWrapper<E1, E2>(iterator);

 	}

 

@@ -641,7 +661,10 @@ public final class IteratorTools {
 	 * Return a list iterator that converts the specified iterator's element type.

 	 * @see LateralListIteratorWrapper

 	 */

-	public static <E1, E2> LateralListIteratorWrapper<E1, E2> cast(ListIterator<E1> iterator) {

+	public static <E1, E2> ListIterator<E2> cast(ListIterator<E1> iterator) {

+		if (isEmpty(iterator)) {

+			return emptyListIterator();

+		}

 		return new LateralListIteratorWrapper<E1, E2>(iterator);

 	}

 

@@ -649,7 +672,10 @@ public final class IteratorTools {
 	 * Return an iterator that converts the specified iterator's element type.

 	 * @see SubIteratorWrapper

 	 */

-	public static <E1, E2 extends E1> SubIteratorWrapper<E1, E2> downCast(Iterator<E1> iterator) {

+	public static <E1, E2 extends E1> Iterator<E2> downCast(Iterator<E1> iterator) {

+		if (isEmpty(iterator)) {

+			return emptyIterator();

+		}

 		return new SubIteratorWrapper<E1, E2>(iterator);

 	}

 

@@ -657,7 +683,10 @@ public final class IteratorTools {
 	 * Return an iterator that converts the specified iterator's element type.

 	 * @see SubListIteratorWrapper

 	 */

-	public static <E1, E2 extends E1> SubListIteratorWrapper<E1, E2> downCast(ListIterator<E1> iterator) {

+	public static <E1, E2 extends E1> ListIterator<E2> downCast(ListIterator<E1> iterator) {

+		if (isEmpty(iterator)) {

+			return emptyListIterator();

+		}

 		return new SubListIteratorWrapper<E1, E2>(iterator);

 	}

 

@@ -666,6 +695,9 @@ public final class IteratorTools {
 	 * @see SuperIteratorWrapper

 	 */

 	public static <E> Iterator<E> upCast(Iterator<? extends E> iterator) {

+		if (isEmpty(iterator)) {

+			return emptyIterator();

+		}

 		return new SuperIteratorWrapper<E>(iterator);

 	}

 

@@ -674,6 +706,9 @@ public final class IteratorTools {
 	 * @see SuperListIteratorWrapper

 	 */

 	public static <E> ListIterator<E> upCast(ListIterator<? extends E> iterator) {

+		if (isEmpty(iterator)) {

+			return emptyListIterator();

+		}

 		return new SuperListIteratorWrapper<E>(iterator);

 	}

 

@@ -682,7 +717,10 @@ public final class IteratorTools {
 	 * the specified {@link Transformer transformer}.

 	 * @see ChainIterator

 	 */

-	public static <E> ChainIterator<E> chainIterator(E first, Transformer<? super E, ? extends E> transformer) {

+	public static <E> Iterator<E> chainIterator(E first, Transformer<? super E, ? extends E> transformer) {

+		if (first == null) {

+			return emptyIterator();

+		}

 		return new ChainIterator<E>(first, transformer);

 	}

 

@@ -691,7 +729,7 @@ public final class IteratorTools {
 	 * elements.

 	 * @see CloneIterator

 	 */

-	public static <E> CloneIterator<E> clone(Collection<? extends E> collection) {

+	public static <E> Iterator<E> clone(Collection<? extends E> collection) {

 		return clone(collection, DisabledClosure.instance());

 	}

 

@@ -700,7 +738,10 @@ public final class IteratorTools {
 	 * elements and uses the specified {@link Closure remove closure}.

 	 * @see CloneIterator

 	 */

-	public static <E> CloneIterator<E> clone(Collection<? extends E> collection, Closure<? super E> removeClosure) {

+	public static <E> Iterator<E> clone(Collection<? extends E> collection, Closure<? super E> removeClosure) {

+		if (collection.isEmpty()) {

+			return emptyIterator();

+		}

 		return new CloneIterator<E>(collection, removeClosure);

 	}

 

@@ -709,7 +750,7 @@ public final class IteratorTools {
 	 * elements.

 	 * @see CloneIterator

 	 */

-	public static <E> CloneListIterator<E> clone(List<? extends E> list) {

+	public static <E> ListIterator<E> clone(List<? extends E> list) {

 		return clone(list, Adapter.ReadOnly.<E>instance());

 	}

 

@@ -718,7 +759,10 @@ public final class IteratorTools {
 	 * elements and uses the specified {@link CloneListIterator.Adapter adapter}.

 	 * @see CloneIterator

 	 */

-	public static <E> CloneListIterator<E> clone(List<? extends E> list, CloneListIterator.Adapter<E> adapter) {

+	public static <E> ListIterator<E> clone(List<? extends E> list, CloneListIterator.Adapter<E> adapter) {

+		if (list.isEmpty()) {

+			return emptyListIterator();

+		}

 		return new CloneListIterator<E>(list, adapter);

 	}

 

@@ -728,8 +772,11 @@ public final class IteratorTools {
 	 * @see CompositeIterator

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> CompositeIterator<E> add(Iterator<? extends E> iterator, E object) {

-		return concatenate(iterator, singletonIterator(object));

+	public static <E> Iterator<E> add(Iterator<? extends E> iterator, E object) {

+		if (isEmpty(iterator)) {

+			return singletonIterator(object);

+		}

+		return concatenate_(iterator, singletonIterator(object));

 	}

 

 	/**

@@ -738,8 +785,11 @@ public final class IteratorTools {
 	 * @see CompositeIterator

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> CompositeIterator<E> insert(E object, Iterator<? extends E> iterator) {

-		return concatenate(singletonIterator(object), iterator);

+	public static <E> Iterator<E> insert(E object, Iterator<? extends E> iterator) {

+		if (isEmpty(iterator)) {

+			return singletonIterator(object);

+		}

+		return concatenate_(singletonIterator(object), iterator);

 	}

 

 	/**

@@ -747,8 +797,23 @@ public final class IteratorTools {
 	 * elements in the specified iterators.

 	 * @see CompositeIterator

 	 */

-	public static <E> CompositeIterator<E> concatenate(Iterator<? extends E>... iterators) {

-		return concatenate(iterator(iterators));

+	@SuppressWarnings("unchecked")

+	public static <E> Iterator<E> concatenate(Iterator<? extends E>... iterators) {

+		int len = iterators.length;

+		if (len == 0) {

+			return emptyIterator();

+		}

+		if (len == 1) {

+			return (Iterator<E>) iterators[0];

+		}

+		return concatenate_(iterators);

+	}

+

+	/**

+	 * assume the list is not empty

+	 */

+	private static <E> Iterator<E> concatenate_(Iterator<? extends E>... iterators) {

+		return concatenate_(iterator(iterators));

 	}

 

 	/**

@@ -756,7 +821,17 @@ public final class IteratorTools {
 	 * elements in the specified iterators.

 	 * @see CompositeIterator

 	 */

-	public static <E> CompositeIterator<E> concatenate(Iterator<? extends Iterator<? extends E>> iterators) {

+	public static <E> Iterator<E> concatenate(Iterator<? extends Iterator<? extends E>> iterators) {

+		if (isEmpty(iterators)) {

+			return emptyListIterator();

+		}

+		return concatenate_(iterators);

+	}

+

+	/**

+	 * assume the list is not empty

+	 */

+	private static <E> Iterator<E> concatenate_(Iterator<? extends Iterator<? extends E>> iterators) {

 		return new CompositeIterator<E>(iterators);

 	}

 

@@ -765,7 +840,7 @@ public final class IteratorTools {
 	 * Use the specified transformer to transform each parent into its children.

 	 * @see CompositeIterator

 	 */

-	public static <P, E> CompositeIterator<E> children(Iterator<? extends P> parents, Transformer<? super P, ? extends Iterator<? extends E>> childrenTransformer) {

+	public static <P, E> Iterator<E> children(Iterator<? extends P> parents, Transformer<? super P, ? extends Iterator<? extends E>> childrenTransformer) {

 		return concatenate(transform(parents, childrenTransformer));

 	}

 

@@ -775,8 +850,11 @@ public final class IteratorTools {
 	 * @see CompositeListIterator

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> CompositeListIterator<E> add(ListIterator<E> iterator, E object) {

-		return concatenate(iterator, singletonListIterator(object));

+	public static <E> ListIterator<E> add(ListIterator<E> iterator, E object) {

+		if (isEmpty(iterator)) {

+			return singletonListIterator(object);

+		}

+		return concatenate_(iterator, singletonListIterator(object));

 	}

 

 	/**

@@ -785,8 +863,11 @@ public final class IteratorTools {
 	 * @see CompositeListIterator

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> CompositeListIterator<E> insert(E object, ListIterator<E> iterator) {

-		return concatenate(singletonListIterator(object), iterator);

+	public static <E> ListIterator<E> insert(E object, ListIterator<E> iterator) {

+		if (isEmpty(iterator)) {

+			return singletonListIterator(object);

+		}

+		return concatenate_(singletonListIterator(object), iterator);

 	}

 

 	/**

@@ -794,8 +875,22 @@ public final class IteratorTools {
 	 * elements in the specified iterators.

 	 * @see CompositeListIterator

 	 */

-	public static <E> CompositeListIterator<E> concatenate(ListIterator<E>... iterators) {

-		return concatenate(listIterator(iterators));

+	public static <E> ListIterator<E> concatenate(ListIterator<E>... iterators) {

+		int len = iterators.length;

+		if (len == 0) {

+			return emptyListIterator();

+		}

+		if (len == 1) {

+			return iterators[0];

+		}

+		return concatenate_(iterators);

+	}

+

+	/**

+	 * assume the list is not empty

+	 */

+	private static <E> ListIterator<E> concatenate_(ListIterator<E>... iterators) {

+		return concatenate_(listIterator(iterators));

 	}

 

 	/**

@@ -803,7 +898,17 @@ public final class IteratorTools {
 	 * elements in the specified iterators.

 	 * @see CompositeListIterator

 	 */

-	public static <E> CompositeListIterator<E> concatenate(ListIterator<? extends ListIterator<E>> iterators) {

+	public static <E> ListIterator<E> concatenate(ListIterator<? extends ListIterator<E>> iterators) {

+		if (isEmpty(iterators)) {

+			return emptyListIterator();

+		}

+		return concatenate_(iterators);

+	}

+

+	/**

+	 * assume the list is not empty

+	 */

+	private static <E> ListIterator<E> concatenate_(ListIterator<? extends ListIterator<E>> iterators) {

 		return new CompositeListIterator<E>(iterators);

 	}

 

@@ -812,7 +917,7 @@ public final class IteratorTools {
 	 * Use the specified transformer to transform each parent into its children.

 	 * @see CompositeListIterator

 	 */

-	public static <P, E> CompositeListIterator<E> children(ListIterator<? extends P> parents, Transformer<? super P, ? extends ListIterator<E>> childrenTransformer) {

+	public static <P, E> ListIterator<E> children(ListIterator<? extends P> parents, Transformer<? super P, ? extends ListIterator<E>> childrenTransformer) {

 		return concatenate(transform(parents, childrenTransformer));

 	}

 

@@ -822,8 +927,11 @@ public final class IteratorTools {
 	 * @see ReadOnlyCompositeListIterator

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> ReadOnlyCompositeListIterator<E> addReadOnly(ListIterator<? extends E> iterator, E object) {

-		return concatenateReadOnly(iterator, singletonListIterator(object));

+	public static <E> ListIterator<E> addReadOnly(ListIterator<? extends E> iterator, E object) {

+		if (isEmpty(iterator)) {

+			return singletonListIterator(object);

+		}

+		return concatenateReadOnly_(iterator, singletonListIterator(object));

 	}

 

 	/**

@@ -832,8 +940,11 @@ public final class IteratorTools {
 	 * @see ReadOnlyCompositeListIterator

 	 */

 	@SuppressWarnings("unchecked")

-	public static <E> ReadOnlyCompositeListIterator<E> insertReadOnly(E object, ListIterator<? extends E> iterator) {

-		return concatenateReadOnly(singletonListIterator(object), iterator);

+	public static <E> ListIterator<E> insertReadOnly(E object, ListIterator<? extends E> iterator) {

+		if (isEmpty(iterator)) {

+			return singletonListIterator(object);

+		}

+		return concatenateReadOnly_(singletonListIterator(object), iterator);

 	}

 

 	/**

@@ -841,8 +952,23 @@ public final class IteratorTools {
 	 * elements in the specified iterators.

 	 * @see ReadOnlyCompositeListIterator

 	 */

-	public static <E> ReadOnlyCompositeListIterator<E> concatenateReadOnly(ListIterator<? extends E>... iterators) {

-		return concatenateReadOnly(listIterator(iterators));

+	@SuppressWarnings("unchecked")

+	public static <E> ListIterator<E> concatenateReadOnly(ListIterator<? extends E>... iterators) {

+		int len = iterators.length;

+		if (len == 0) {

+			return emptyListIterator();

+		}

+		if (len == 1) {

+			return (ListIterator<E>) iterators[0];

+		}

+		return concatenateReadOnly_(iterators);

+	}

+

+	/**

+	 * assume the list is not empty

+	 */

+	private static <E> ListIterator<E> concatenateReadOnly_(ListIterator<? extends E>... iterators) {

+		return concatenateReadOnly_(listIterator(iterators));

 	}

 

 	/**

@@ -850,7 +976,17 @@ public final class IteratorTools {
 	 * elements in the specified iterators.

 	 * @see ReadOnlyCompositeListIterator

 	 */

-	public static <E> ReadOnlyCompositeListIterator<E> concatenateReadOnly(ListIterator<? extends ListIterator<? extends E>> iterators) {

+	public static <E> ListIterator<E> concatenateReadOnly(ListIterator<? extends ListIterator<? extends E>> iterators) {

+		if (isEmpty(iterators)) {

+			return emptyListIterator();

+		}

+		return concatenateReadOnly_(iterators);

+	}

+

+	/**

+	 * assume the list is not empty

+	 */

+	private static <E> ListIterator<E> concatenateReadOnly_(ListIterator<? extends ListIterator<? extends E>> iterators) {

 		return new ReadOnlyCompositeListIterator<E>(iterators);

 	}

 

@@ -859,7 +995,7 @@ public final class IteratorTools {
 	 * Use the specified transformer to transform each parent into its children.

 	 * @see ReadOnlyCompositeListIterator

 	 */

-	public static <P, E> ReadOnlyCompositeListIterator<E> readOnlyChildren(ListIterator<? extends P> parents, Transformer<? super P, ? extends ListIterator<? extends E>> childrenTransformer) {

+	public static <P, E> ListIterator<E> readOnlyChildren(ListIterator<? extends P> parents, Transformer<? super P, ? extends ListIterator<? extends E>> childrenTransformer) {

 		return concatenateReadOnly(transform(parents, childrenTransformer));

 	}

 

@@ -882,7 +1018,10 @@ public final class IteratorTools {
 	 * elements in the specified iterator.

 	 * @see FilteringIterator

 	 */

-	public static <E> FilteringIterator<E> filter(Iterator<? extends E> iterator, Predicate<? super E> predicate) {

+	public static <E> Iterator<E> filter(Iterator<? extends E> iterator, Predicate<? super E> predicate) {

+		if (isEmpty(iterator)) {

+			return emptyIterator();

+		}

 		return new FilteringIterator<E>(iterator, predicate);

 	}

 

@@ -891,7 +1030,7 @@ public final class IteratorTools {
 	 * elements in the specified iterator.

 	 * @see FilteringIterator

 	 */

-	public static <E> FilteringIterator<E> removeNulls(Iterator<? extends E> iterator) {

+	public static <E> Iterator<E> removeNulls(Iterator<? extends E> iterator) {

 		return filter(iterator, PredicateTools.isNotNull());

 	}

 

@@ -900,8 +1039,8 @@ public final class IteratorTools {
 	 * by its children etc. as determined by the specified transformer.

 	 * @see GraphIterator

 	 */

-	public static <E> GraphIterator<E> graphIterator(E root, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

-		return graphIterator(singletonIterator(root), transformer);

+	public static <E> Iterator<E> graphIterator(E root, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

+		return graphIterator_(singletonIterator(root), transformer);

 	}

 

 	/**

@@ -909,8 +1048,11 @@ public final class IteratorTools {
 	 * by their children etc. as determined by the specified transformer.

 	 * @see GraphIterator

 	 */

-	public static <E> GraphIterator<E> graphIterator(E[] roots, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

-		return graphIterator(iterator(roots), transformer);

+	public static <E> Iterator<E> graphIterator(E[] roots, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

+		if (roots.length == 0) {

+			return emptyIterator();

+		}

+		return graphIterator_(iterator(roots), transformer);

 	}

 

 	/**

@@ -918,21 +1060,34 @@ public final class IteratorTools {
 	 * by their children etc. as determined by the specified transformer.

 	 * @see GraphIterator

 	 */

-	public static <E> GraphIterator<E> graphIterator(Iterator<? extends E> roots, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

+	public static <E> Iterator<E> graphIterator(Iterator<? extends E> roots, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

+		if (isEmpty(roots)) {

+			return emptyIterator();

+		}

+		return graphIterator_(roots, transformer);

+	}

+

+	/**

+	 * assume roots are present

+	 */

+	private static <E> Iterator<E> graphIterator_(Iterator<? extends E> roots, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

 		return new GraphIterator<E>(roots, transformer);

 	}

 

 	/**

 	 * Return an iterator the corresponds to the specified enumeration.

 	 */

-	public static <E> EnumerationIterator<E> iterator(Enumeration<E> enumeration) {

+	public static <E> Iterator<E> iterator(Enumeration<E> enumeration) {

+		if (EnumerationTools.isEmpty(enumeration)) {

+			return emptyIterator();

+		}

 		return new EnumerationIterator<E>(enumeration);

 	}

 

 	/**

 	 * Return an iterator on the elements in the specified array.

 	 */

-	public static <E> ArrayIterator<E> iterator(E... array) {

+	public static <E> Iterator<E> iterator(E... array) {

 		return iterator(array, 0);

 	}

 

@@ -940,7 +1095,7 @@ public final class IteratorTools {
 	 * Return an iterator on the elements in the specified array

 	 * starting at the specified position in the array.

 	 */

-	public static <E> ArrayIterator<E> iterator(E[] array, int start) {

+	public static <E> Iterator<E> iterator(E[] array, int start) {

 		return iterator(array, start, array.length);

 	}

 

@@ -949,7 +1104,10 @@ public final class IteratorTools {
 	 * starting at the specified start index, inclusive, and continuing to

 	 * the specified end index, exclusive.

 	 */

-	public static <E> ArrayIterator<E> iterator(E[] array, int start, int end) {

+	public static <E> Iterator<E> iterator(E[] array, int start, int end) {

+		if (start == end) {

+			return emptyIterator();

+		}

 		return new ArrayIterator<E>(array, start, end);

 	}

 

@@ -957,7 +1115,7 @@ public final class IteratorTools {
 	 * Return an iterator on the specified queue.

 	 * @see Queue

 	 */

-	public static <E> QueueIterator<E> iterator(Queue<? extends E> queue) {

+	public static <E> Iterator<E> iterator(Queue<? extends E> queue) {

 		return new QueueIterator<E>(queue);

 	}

 

@@ -965,14 +1123,14 @@ public final class IteratorTools {
 	 * Return an iterator on the specified stack.

 	 * @see Stack

 	 */

-	public static <E> StackIterator<E> iterator(Stack<? extends E> stack) {

+	public static <E> Iterator<E> iterator(Stack<? extends E> stack) {

 		return new StackIterator<E>(stack);

 	}

 

 	/**

 	 * Return a list iterator for the specified array.

 	 */

-	public static <E> ArrayListIterator<E> listIterator(E... array) {

+	public static <E> ListIterator<E> listIterator(E... array) {

 		return listIterator(array, 0);

 	}

 

@@ -980,7 +1138,7 @@ public final class IteratorTools {
 	 * Return a list iterator for the specified array

 	 * starting at the specified position in the array.

 	 */

-	public static <E> ArrayListIterator<E> listIterator(E[] array, int start) {

+	public static <E> ListIterator<E> listIterator(E[] array, int start) {

 		return listIterator(array, start, array.length);

 	}

 

@@ -989,7 +1147,10 @@ public final class IteratorTools {
 	 * starting at the specified start index, inclusive, and continuing to

 	 * the specified end index, exclusive.

 	 */

-	public static <E> ArrayListIterator<E> listIterator(E[] array, int start, int end) {

+	public static <E> ListIterator<E> listIterator(E[] array, int start, int end) {

+		if (start == end) {

+			return emptyListIterator();

+		}

 		return new ArrayListIterator<E>(array, start, end);

 	}

 

@@ -997,7 +1158,10 @@ public final class IteratorTools {
 	 * Return an iterator the returns <code>null</code> the specified number of times.

 	 * @see NullElementIterator

 	 */

-	public static <E> NullElementIterator<E> nullElementIterator(int size) {

+	public static <E> Iterator<E> nullElementIterator(int size) {

+		if (size == 0) {

+			return emptyIterator();

+		}

 		return new NullElementIterator<E>(size);

 	}

 

@@ -1005,7 +1169,10 @@ public final class IteratorTools {
 	 * Return a list iterator the returns <code>null</code> the specified number of times.

 	 * @see NullElementListIterator

 	 */

-	public static <E> NullElementListIterator<E> nullElementListIterator(int size) {

+	public static <E> ListIterator<E> nullElementListIterator(int size) {

+		if (size == 0) {

+			return emptyListIterator();

+		}

 		return new NullElementListIterator<E>(size);

 	}

 

@@ -1020,7 +1187,10 @@ public final class IteratorTools {
 	 * Convert the specified iterator to read-only.

 	 * @see ReadOnlyIterator

 	 */

-	public static <E> ReadOnlyIterator<E> readOnly(Iterator<? extends E> iterator) {

+	public static <E> Iterator<E> readOnly(Iterator<? extends E> iterator) {

+		if (isEmpty(iterator)) {

+			return emptyIterator();

+		}

 		return new ReadOnlyIterator<E>(iterator);

 	}

 

@@ -1028,7 +1198,10 @@ public final class IteratorTools {
 	 * Convert the specified iterator to read-only.

 	 * @see ReadOnlyListIterator

 	 */

-	public static <E> ReadOnlyListIterator<E> readOnly(ListIterator<? extends E> iterator) {

+	public static <E> ListIterator<E> readOnly(ListIterator<? extends E> iterator) {

+		if (isEmpty(iterator)) {

+			return emptyListIterator();

+		}

 		return new ReadOnlyListIterator<E>(iterator);

 	}

 

@@ -1037,7 +1210,10 @@ public final class IteratorTools {
 	 * of times.

 	 * @see RepeatingElementIterator

 	 */

-	public static <E> RepeatingElementIterator<E> repeatingElementIterator(E element, int size) {

+	public static <E> Iterator<E> repeatingElementIterator(E element, int size) {

+		if (size == 0) {

+			return emptyIterator();

+		}

 		return new RepeatingElementIterator<E>(element, size);

 	}

 

@@ -1046,7 +1222,10 @@ public final class IteratorTools {
 	 * of times.

 	 * @see RepeatingElementIterator

 	 */

-	public static <E> RepeatingElementListIterator<E> repeatingElementListIterator(E element, int size) {

+	public static <E> ListIterator<E> repeatingElementListIterator(E element, int size) {

+		if (size == 0) {

+			return emptyListIterator();

+		}

 		return new RepeatingElementListIterator<E>(element, size);

 	}

 

@@ -1054,7 +1233,10 @@ public final class IteratorTools {
 	 * Return an iterator that returns the objects in the specified iterator

 	 * in reverse order.

 	 */

-	public static <E> ReverseIterator<E> reverse(Iterator<? extends E> iterator) {

+	public static <E> Iterator<E> reverse(Iterator<? extends E> iterator) {

+		if (isEmpty(iterator)) {

+			return emptyIterator();

+		}

 		return new ReverseIterator<E>(iterator);

 	}

 

@@ -1063,7 +1245,10 @@ public final class IteratorTools {
 	 * in reverse order.

 	 * The specified iterator size is a performance hint.

 	 */

-	public static <E> ReverseIterator<E> reverse(Iterator<? extends E> iterator, int iteratorSize) {

+	public static <E> Iterator<E> reverse(Iterator<? extends E> iterator, int iteratorSize) {

+		if (isEmpty(iterator)) {

+			return emptyIterator();

+		}

 		return new ReverseIterator<E>(iterator, iteratorSize);

 	}

 

@@ -1072,7 +1257,7 @@ public final class IteratorTools {
 	 * specified object.

 	 * @see SingleElementIterator

 	 */

-	public static <E> SingleElementIterator<E> singletonIterator(E value) {

+	public static <E> Iterator<E> singletonIterator(E value) {

 		return new SingleElementIterator<E>(value);

 	}

 

@@ -1081,7 +1266,7 @@ public final class IteratorTools {
 	 * specified object.

 	 * @see SingleElementListIterator

 	 */

-	public static <E> SingleElementListIterator<E> singletonListIterator(E value) {

+	public static <E> ListIterator<E> singletonListIterator(E value) {

 		return new SingleElementListIterator<E>(value);

 	}

 

@@ -1089,7 +1274,10 @@ public final class IteratorTools {
 	 * Return an iterator that synchronizes the specified iterator on itself.

 	 * @see SynchronizedIterator

 	 */

-	public static <E> SynchronizedIterator<E> synchronize(Iterator<? extends E> iterator) {

+	public static <E> Iterator<E> synchronize(Iterator<? extends E> iterator) {

+		if (isEmpty(iterator)) {

+			return emptyIterator();

+		}

 		return new SynchronizedIterator<E>(iterator);

 	}

 

@@ -1098,7 +1286,10 @@ public final class IteratorTools {
 	 * specified mutex.

 	 * @see SynchronizedIterator

 	 */

-	public static <E> SynchronizedIterator<E> synchronize(Iterator<? extends E> iterator, Object mutex) {

+	public static <E> Iterator<E> synchronize(Iterator<? extends E> iterator, Object mutex) {

+		if (isEmpty(iterator)) {

+			return emptyIterator();

+		}

 		return new SynchronizedIterator<E>(iterator, mutex);

 	}

 

@@ -1106,7 +1297,10 @@ public final class IteratorTools {
 	 * Return an iterator that synchronizes the specified iterator on itself.

 	 * @see SynchronizedListIterator

 	 */

-	public static <E> SynchronizedListIterator<E> synchronize(ListIterator<E> iterator) {

+	public static <E> ListIterator<E> synchronize(ListIterator<E> iterator) {

+		if (isEmpty(iterator)) {

+			return emptyListIterator();

+		}

 		return new SynchronizedListIterator<E>(iterator);

 	}

 

@@ -1115,7 +1309,10 @@ public final class IteratorTools {
 	 * specified mutex.

 	 * @see SynchronizedListIterator

 	 */

-	public static <E> SynchronizedListIterator<E> synchronize(ListIterator<E> iterator, Object mutex) {

+	public static <E> ListIterator<E> synchronize(ListIterator<E> iterator, Object mutex) {

+		if (isEmpty(iterator)) {

+			return emptyListIterator();

+		}

 		return new SynchronizedListIterator<E>(iterator, mutex);

 	}

 

@@ -1124,7 +1321,10 @@ public final class IteratorTools {
 	 * elements in the specified iterator.

 	 * @see TransformationIterator

 	 */

-	public static <E1, E2> TransformationIterator<E1, E2> transform(Iterator<? extends E1> iterator, Transformer<? super E1, ? extends E2> transformer) {

+	public static <E1, E2> Iterator<E2> transform(Iterator<? extends E1> iterator, Transformer<? super E1, ? extends E2> transformer) {

+		if (isEmpty(iterator)) {

+			return emptyIterator();

+		}

 		return new TransformationIterator<E1, E2>(iterator, transformer);

 	}

 

@@ -1133,7 +1333,10 @@ public final class IteratorTools {
 	 * elements in the specified iterator.

 	 * @see TransformationListIterator

 	 */

-	public static <E1, E2> TransformationListIterator<E1, E2> transform(ListIterator<? extends E1> iterator, Transformer<? super E1, ? extends E2> transformer) {

+	public static <E1, E2> ListIterator<E2> transform(ListIterator<? extends E1> iterator, Transformer<? super E1, ? extends E2> transformer) {

+		if (isEmpty(iterator)) {

+			return emptyListIterator();

+		}

 		return new TransformationListIterator<E1, E2>(iterator, transformer);

 	}

 

@@ -1142,8 +1345,8 @@ public final class IteratorTools {
 	 * with the specified root and transformer.

 	 * @see TreeIterator

 	 */

-	public static <E> TreeIterator<E> treeIterator(E root, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

-		return treeIterator(singletonIterator(root), transformer);

+	public static <E> Iterator<E> treeIterator(E root, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

+		return treeIterator_(singletonIterator(root), transformer);

 	}

 

 	/**

@@ -1151,8 +1354,11 @@ public final class IteratorTools {
 	 * with the specified roots and transformer.

 	 * @see TreeIterator

 	 */

-	public static <E> TreeIterator<E> treeIterator(E[] roots, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

-		return treeIterator(iterator(roots), transformer);

+	public static <E> Iterator<E> treeIterator(E[] roots, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

+		if (roots.length == 0) {

+			return emptyIterator();

+		}

+		return treeIterator_(iterator(roots), transformer);

 	}

 

 	/**

@@ -1160,10 +1366,33 @@ public final class IteratorTools {
 	 * with the specified roots and transformer.

 	 * @see TreeIterator

 	 */

-	public static <E> TreeIterator<E> treeIterator(Iterator<? extends E> roots, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

+	public static <E> Iterator<E> treeIterator(Iterator<? extends E> roots, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

+		if (isEmpty(roots)) {

+			return emptyIterator();

+		}

+		return treeIterator_(roots, transformer);

+	}

+

+	/**

+	 * assume roots are present

+	 */

+	private static <E> Iterator<E> treeIterator_(Iterator<? extends E> roots, Transformer<? super E, ? extends Iterator<? extends E>> transformer) {

 		return new TreeIterator<E>(roots, transformer);

 	}

 

+	/**

+	 * Return a string representation of the specified iterator.

+	 */

+	public static String toString(Iterator<?> iterator) {

+		StringBuilder sb = new StringBuilder();

+		sb.append('[');

+		while (iterator.hasNext()) {

+			sb.append(iterator.next());

+		}

+		sb.append(']');

+		return sb.toString();

+	}

+

 

 	// ********** constructor **********