Java tutorial
/* * Copyright 2002-2004 The Apache Software Foundation * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.collections; import java.lang.reflect.Array; import java.lang.reflect.Method; import java.util.ArrayList; import java.util.Collection; import java.util.Comparator; import java.util.Dictionary; import java.util.Enumeration; import java.util.Iterator; import java.util.List; import java.util.ListIterator; import java.util.Map; import org.apache.commons.collections.iterators.ArrayIterator; import org.apache.commons.collections.iterators.ArrayListIterator; import org.apache.commons.collections.iterators.CollatingIterator; import org.apache.commons.collections.iterators.EmptyIterator; import org.apache.commons.collections.iterators.EmptyListIterator; import org.apache.commons.collections.iterators.EmptyMapIterator; import org.apache.commons.collections.iterators.EmptyOrderedIterator; import org.apache.commons.collections.iterators.EmptyOrderedMapIterator; import org.apache.commons.collections.iterators.EnumerationIterator; import org.apache.commons.collections.iterators.FilterIterator; import org.apache.commons.collections.iterators.FilterListIterator; import org.apache.commons.collections.iterators.IteratorChain; import org.apache.commons.collections.iterators.IteratorEnumeration; import org.apache.commons.collections.iterators.ListIteratorWrapper; import org.apache.commons.collections.iterators.LoopingIterator; import org.apache.commons.collections.iterators.LoopingListIterator; import org.apache.commons.collections.iterators.ObjectArrayIterator; import org.apache.commons.collections.iterators.ObjectArrayListIterator; import org.apache.commons.collections.iterators.ObjectGraphIterator; import org.apache.commons.collections.iterators.SingletonIterator; import org.apache.commons.collections.iterators.SingletonListIterator; import org.apache.commons.collections.iterators.TransformIterator; import org.apache.commons.collections.iterators.UnmodifiableIterator; import org.apache.commons.collections.iterators.UnmodifiableListIterator; import org.apache.commons.collections.iterators.UnmodifiableMapIterator; /** * Provides static utility methods and decorators for {@link Iterator} * instances. The implementations are provided in the iterators subpackage. * <p> * WARNING: Due to human error certain binary incompatabilities were introduced * between Commons Collections 2.1 and 3.0. The class remained source and test * compatible, so if you can recompile all your classes and dependencies * everything is OK. Those methods which are binary incompatible are marked as * such, together with alternate solutions that are binary compatible * against versions 2.1.1 and 3.1. * * @since Commons Collections 2.1 * @version $Revision: 1.28 $ $Date: 2004/07/17 21:08:05 $ * * @author Stephen Colebourne * @author Phil Steitz */ public class IteratorUtils { // validation is done in this class in certain cases because the // public classes allow invalid states /** * An iterator over no elements. * <p> * WARNING: This constant is binary incompatible with Commons Collections 2.1 and 2.1.1. * Use <code>EmptyIterator.INSTANCE</code> for compatability with Commons Collections 2.1.1. */ public static final ResettableIterator EMPTY_ITERATOR = EmptyIterator.RESETTABLE_INSTANCE; /** * A list iterator over no elements. * <p> * WARNING: This constant is binary incompatible with Commons Collections 2.1 and 2.1.1. * Use <code>EmptyListIterator.INSTANCE</code> for compatability with Commons Collections 2.1.1. */ public static final ResettableListIterator EMPTY_LIST_ITERATOR = EmptyListIterator.RESETTABLE_INSTANCE; /** * An ordered iterator over no elements. */ public static final OrderedIterator EMPTY_ORDERED_ITERATOR = EmptyOrderedIterator.INSTANCE; /** * A map iterator over no elements. */ public static final MapIterator EMPTY_MAP_ITERATOR = EmptyMapIterator.INSTANCE; /** * An ordered map iterator over no elements. */ public static final OrderedMapIterator EMPTY_ORDERED_MAP_ITERATOR = EmptyOrderedMapIterator.INSTANCE; /** * IteratorUtils is not normally instantiated. */ public IteratorUtils() { } // Empty //----------------------------------------------------------------------- /** * Gets an empty iterator. * <p> * This iterator is a valid iterator object that will iterate over * nothing. * <p> * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. * Use <code>EmptyIterator.INSTANCE</code> for compatability with Commons Collections 2.1.1. * * @return an iterator over nothing */ public static ResettableIterator emptyIterator() { return EMPTY_ITERATOR; } /** * Gets an empty list iterator. * <p> * This iterator is a valid list iterator object that will iterate * over nothing. * <p> * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. * Use <code>EmptyListIterator.INSTANCE</code> for compatability with Commons Collections 2.1.1. * * @return a list iterator over nothing */ public static ResettableListIterator emptyListIterator() { return EMPTY_LIST_ITERATOR; } /** * Gets an empty ordered iterator. * <p> * This iterator is a valid iterator object that will iterate * over nothing. * * @return an ordered iterator over nothing */ public static OrderedIterator emptyOrderedIterator() { return EMPTY_ORDERED_ITERATOR; } /** * Gets an empty map iterator. * <p> * This iterator is a valid map iterator object that will iterate * over nothing. * * @return a map iterator over nothing */ public static MapIterator emptyMapIterator() { return EMPTY_MAP_ITERATOR; } /** * Gets an empty ordered map iterator. * <p> * This iterator is a valid map iterator object that will iterate * over nothing. * * @return a map iterator over nothing */ public static OrderedMapIterator emptyOrderedMapIterator() { return EMPTY_ORDERED_MAP_ITERATOR; } // Singleton //----------------------------------------------------------------------- /** * Gets a singleton iterator. * <p> * This iterator is a valid iterator object that will iterate over * the specified object. * <p> * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. * Use <code>new SingletonIterator(object)</code> for compatability. * * @param object the single object over which to iterate * @return a singleton iterator over the object */ public static ResettableIterator singletonIterator(Object object) { return new SingletonIterator(object); } /** * Gets a singleton list iterator. * <p> * This iterator is a valid list iterator object that will iterate over * the specified object. * * @param object the single object over which to iterate * @return a singleton list iterator over the object */ public static ListIterator singletonListIterator(Object object) { return new SingletonListIterator(object); } // Arrays //----------------------------------------------------------------------- /** * Gets an iterator over an object array. * <p> * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. * Use <code>new ArrayIterator(array)</code> for compatability. * * @param array the array over which to iterate * @return an iterator over the array * @throws NullPointerException if array is null */ public static ResettableIterator arrayIterator(Object[] array) { return new ObjectArrayIterator(array); } /** * Gets an iterator over an object or primitive array. * <p> * This method will handle primitive arrays as well as object arrays. * The primitives will be wrapped in the appropriate wrapper class. * * @param array the array over which to iterate * @return an iterator over the array * @throws IllegalArgumentException if the array is not an array * @throws NullPointerException if array is null */ public static ResettableIterator arrayIterator(Object array) { return new ArrayIterator(array); } /** * Gets an iterator over the end part of an object array. * <p> * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. * Use <code>new ArrayIterator(array,start)</code> for compatability. * * @param array the array over which to iterate * @param start the index to start iterating at * @return an iterator over part of the array * @throws IndexOutOfBoundsException if start is less than zero or greater * than the length of the array * @throws NullPointerException if array is null */ public static ResettableIterator arrayIterator(Object[] array, int start) { return new ObjectArrayIterator(array, start); } /** * Gets an iterator over the end part of an object or primitive array. * <p> * This method will handle primitive arrays as well as object arrays. * The primitives will be wrapped in the appropriate wrapper class. * * @param array the array over which to iterate * @param start the index to start iterating at * @return an iterator over part of the array * @throws IllegalArgumentException if the array is not an array * @throws IndexOutOfBoundsException if start is less than zero or greater * than the length of the array * @throws NullPointerException if array is null */ public static ResettableIterator arrayIterator(Object array, int start) { return new ArrayIterator(array, start); } /** * Gets an iterator over part of an object array. * <p> * WARNING: This method is binary incompatible with Commons Collections 2.1 and 2.1.1. * Use <code>new ArrayIterator(array,start,end)</code> for compatability. * * @param array the array over which to iterate * @param start the index to start iterating at * @param end the index to finish iterating at * @return an iterator over part of the array * @throws IndexOutOfBoundsException if array bounds are invalid * @throws IllegalArgumentException if end is before start * @throws NullPointerException if array is null */ public static ResettableIterator arrayIterator(Object[] array, int start, int end) { return new ObjectArrayIterator(array, start, end); } /** * Gets an iterator over part of an object or primitive array. * <p> * This method will handle primitive arrays as well as object arrays. * The primitives will be wrapped in the appropriate wrapper class. * * @param array the array over which to iterate * @param start the index to start iterating at * @param end the index to finish iterating at * @return an iterator over part of the array * @throws IllegalArgumentException if the array is not an array * @throws IndexOutOfBoundsException if array bounds are invalid * @throws IllegalArgumentException if end is before start * @throws NullPointerException if array is null */ public static ResettableIterator arrayIterator(Object array, int start, int end) { return new ArrayIterator(array, start, end); } //----------------------------------------------------------------------- /** * Gets a list iterator over an object array. * * @param array the array over which to iterate * @return a list iterator over the array * @throws NullPointerException if array is null */ public static ResettableListIterator arrayListIterator(Object[] array) { return new ObjectArrayListIterator(array); } /** * Gets a list iterator over an object or primitive array. * <p> * This method will handle primitive arrays as well as object arrays. * The primitives will be wrapped in the appropriate wrapper class. * * @param array the array over which to iterate * @return a list iterator over the array * @throws IllegalArgumentException if the array is not an array * @throws NullPointerException if array is null */ public static ResettableListIterator arrayListIterator(Object array) { return new ArrayListIterator(array); } /** * Gets a list iterator over the end part of an object array. * * @param array the array over which to iterate * @param start the index to start iterating at * @return a list iterator over part of the array * @throws IndexOutOfBoundsException if start is less than zero * @throws NullPointerException if array is null */ public static ResettableListIterator arrayListIterator(Object[] array, int start) { return new ObjectArrayListIterator(array, start); } /** * Gets a list iterator over the end part of an object or primitive array. * <p> * This method will handle primitive arrays as well as object arrays. * The primitives will be wrapped in the appropriate wrapper class. * * @param array the array over which to iterate * @param start the index to start iterating at * @return a list iterator over part of the array * @throws IllegalArgumentException if the array is not an array * @throws IndexOutOfBoundsException if start is less than zero * @throws NullPointerException if array is null */ public static ResettableListIterator arrayListIterator(Object array, int start) { return new ArrayListIterator(array, start); } /** * Gets a list iterator over part of an object array. * * @param array the array over which to iterate * @param start the index to start iterating at * @param end the index to finish iterating at * @return a list iterator over part of the array * @throws IndexOutOfBoundsException if array bounds are invalid * @throws IllegalArgumentException if end is before start * @throws NullPointerException if array is null */ public static ResettableListIterator arrayListIterator(Object[] array, int start, int end) { return new ObjectArrayListIterator(array, start, end); } /** * Gets a list iterator over part of an object or primitive array. * <p> * This method will handle primitive arrays as well as object arrays. * The primitives will be wrapped in the appropriate wrapper class. * * @param array the array over which to iterate * @param start the index to start iterating at * @param end the index to finish iterating at * @return a list iterator over part of the array * @throws IllegalArgumentException if the array is not an array * @throws IndexOutOfBoundsException if array bounds are invalid * @throws IllegalArgumentException if end is before start * @throws NullPointerException if array is null */ public static ResettableListIterator arrayListIterator(Object array, int start, int end) { return new ArrayListIterator(array, start, end); } // Unmodifiable //----------------------------------------------------------------------- /** * Gets an immutable version of an {@link Iterator}. The returned object * will always throw an {@link UnsupportedOperationException} for * the {@link Iterator#remove} method. * * @param iterator the iterator to make immutable * @return an immutable version of the iterator */ public static Iterator unmodifiableIterator(Iterator iterator) { return UnmodifiableIterator.decorate(iterator); } /** * Gets an immutable version of a {@link ListIterator}. The returned object * will always throw an {@link UnsupportedOperationException} for * the {@link Iterator#remove}, {@link ListIterator#add} and * {@link ListIterator#set} methods. * * @param listIterator the iterator to make immutable * @return an immutable version of the iterator */ public static ListIterator unmodifiableListIterator(ListIterator listIterator) { return UnmodifiableListIterator.decorate(listIterator); } /** * Gets an immutable version of a {@link MapIterator}. The returned object * will always throw an {@link UnsupportedOperationException} for * the {@link Iterator#remove}, {@link MapIterator#setValue(Object)} methods. * * @param mapIterator the iterator to make immutable * @return an immutable version of the iterator */ public static MapIterator unmodifiableMapIterator(MapIterator mapIterator) { return UnmodifiableMapIterator.decorate(mapIterator); } // Chained //----------------------------------------------------------------------- /** * Gets an iterator that iterates through two {@link Iterator}s * one after another. * * @param iterator1 the first iterators to use, not null * @param iterator2 the first iterators to use, not null * @return a combination iterator over the iterators * @throws NullPointerException if either iterator is null */ public static Iterator chainedIterator(Iterator iterator1, Iterator iterator2) { return new IteratorChain(iterator1, iterator2); } /** * Gets an iterator that iterates through an array of {@link Iterator}s * one after another. * * @param iterators the iterators to use, not null or empty or contain nulls * @return a combination iterator over the iterators * @throws NullPointerException if iterators array is null or contains a null */ public static Iterator chainedIterator(Iterator[] iterators) { return new IteratorChain(iterators); } /** * Gets an iterator that iterates through a collections of {@link Iterator}s * one after another. * * @param iterators the iterators to use, not null or empty or contain nulls * @return a combination iterator over the iterators * @throws NullPointerException if iterators collection is null or contains a null * @throws ClassCastException if the iterators collection contains the wrong object type */ public static Iterator chainedIterator(Collection iterators) { return new IteratorChain(iterators); } // Collated //----------------------------------------------------------------------- /** * Gets an iterator that provides an ordered iteration over the elements * contained in a collection of ordered {@link Iterator}s. * <p> * Given two ordered {@link Iterator}s <code>A</code> and <code>B</code>, * the {@link Iterator#next()} method will return the lesser of * <code>A.next()</code> and <code>B.next()</code>. * <p> * The comparator is optional. If null is specified then natural order is used. * * @param comparator the comparator to use, may be null for natural order * @param iterator1 the first iterators to use, not null * @param iterator2 the first iterators to use, not null * @return a combination iterator over the iterators * @throws NullPointerException if either iterator is null */ public static Iterator collatedIterator(Comparator comparator, Iterator iterator1, Iterator iterator2) { return new CollatingIterator(comparator, iterator1, iterator2); } /** * Gets an iterator that provides an ordered iteration over the elements * contained in an array of {@link Iterator}s. * <p> * Given two ordered {@link Iterator}s <code>A</code> and <code>B</code>, * the {@link Iterator#next()} method will return the lesser of * <code>A.next()</code> and <code>B.next()</code> and so on. * <p> * The comparator is optional. If null is specified then natural order is used. * * @param comparator the comparator to use, may be null for natural order * @param iterators the iterators to use, not null or empty or contain nulls * @return a combination iterator over the iterators * @throws NullPointerException if iterators array is null or contains a null */ public static Iterator collatedIterator(Comparator comparator, Iterator[] iterators) { return new CollatingIterator(comparator, iterators); } /** * Gets an iterator that provides an ordered iteration over the elements * contained in a collection of {@link Iterator}s. * <p> * Given two ordered {@link Iterator}s <code>A</code> and <code>B</code>, * the {@link Iterator#next()} method will return the lesser of * <code>A.next()</code> and <code>B.next()</code> and so on. * <p> * The comparator is optional. If null is specified then natural order is used. * * @param comparator the comparator to use, may be null for natural order * @param iterators the iterators to use, not null or empty or contain nulls * @return a combination iterator over the iterators * @throws NullPointerException if iterators collection is null or contains a null * @throws ClassCastException if the iterators collection contains the wrong object type */ public static Iterator collatedIterator(Comparator comparator, Collection iterators) { return new CollatingIterator(comparator, iterators); } // Object Graph //----------------------------------------------------------------------- /** * Gets an iterator that operates over an object graph. * <p> * This iterator can extract multiple objects from a complex tree-like object graph. * The iteration starts from a single root object. * It uses a <code>Transformer</code> to extract the iterators and elements. * Its main benefit is that no intermediate <code>List</code> is created. * <p> * For example, consider an object graph: * <pre> * |- Branch -- Leaf * | \- Leaf * |- Tree | /- Leaf * | |- Branch -- Leaf * Forest | \- Leaf * | |- Branch -- Leaf * | | \- Leaf * |- Tree | /- Leaf * |- Branch -- Leaf * |- Branch -- Leaf</pre> * The following <code>Transformer</code>, used in this class, will extract all * the Leaf objects without creating a combined intermediate list: * <pre> * public Object transform(Object input) { * if (input instanceof Forest) { * return ((Forest) input).treeIterator(); * } * if (input instanceof Tree) { * return ((Tree) input).branchIterator(); * } * if (input instanceof Branch) { * return ((Branch) input).leafIterator(); * } * if (input instanceof Leaf) { * return input; * } * throw new ClassCastException(); * }</pre> * <p> * Internally, iteration starts from the root object. When next is called, * the transformer is called to examine the object. The transformer will return * either an iterator or an object. If the object is an Iterator, the next element * from that iterator is obtained and the process repeats. If the element is an object * it is returned. * <p> * Under many circumstances, linking Iterators together in this manner is * more efficient (and convenient) than using nested for loops to extract a list. * * @param root the root object to start iterating from, null results in an empty iterator * @param transformer the transformer to use, see above, null uses no effect transformer * @return a new object graph iterator * @since Commons Collections 3.1 */ public static Iterator objectGraphIterator(Object root, Transformer transformer) { return new ObjectGraphIterator(root, transformer); } // Transformed //----------------------------------------------------------------------- /** * Gets an iterator that transforms the elements of another iterator. * <p> * The transformation occurs during the next() method and the underlying * iterator is unaffected by the transformation. * * @param iterator the iterator to use, not null * @param transform the transform to use, not null * @return a new transforming iterator * @throws NullPointerException if either parameter is null */ public static Iterator transformedIterator(Iterator iterator, Transformer transform) { if (iterator == null) { throw new NullPointerException("Iterator must not be null"); } if (transform == null) { throw new NullPointerException("Transformer must not be null"); } return new TransformIterator(iterator, transform); } // Filtered //----------------------------------------------------------------------- /** * Gets an iterator that filters another iterator. * <p> * The returned iterator will only return objects that match the specified * filtering predicate. * * @param iterator the iterator to use, not null * @param predicate the predicate to use as a filter, not null * @return a new filtered iterator * @throws NullPointerException if either parameter is null */ public static Iterator filteredIterator(Iterator iterator, Predicate predicate) { if (iterator == null) { throw new NullPointerException("Iterator must not be null"); } if (predicate == null) { throw new NullPointerException("Predicate must not be null"); } return new FilterIterator(iterator, predicate); } /** * Gets a list iterator that filters another list iterator. * <p> * The returned iterator will only return objects that match the specified * filtering predicate. * * @param listIterator the list iterator to use, not null * @param predicate the predicate to use as a filter, not null * @return a new filtered iterator * @throws NullPointerException if either parameter is null */ public static ListIterator filteredListIterator(ListIterator listIterator, Predicate predicate) { if (listIterator == null) { throw new NullPointerException("ListIterator must not be null"); } if (predicate == null) { throw new NullPointerException("Predicate must not be null"); } return new FilterListIterator(listIterator, predicate); } // Looping //----------------------------------------------------------------------- /** * Gets an iterator that loops continuously over the supplied collection. * <p> * The iterator will only stop looping if the remove method is called * enough times to empty the collection, or if the collection is empty * to start with. * * @param coll the collection to iterate over, not null * @return a new looping iterator * @throws NullPointerException if the collection is null */ public static ResettableIterator loopingIterator(Collection coll) { if (coll == null) { throw new NullPointerException("Collection must not be null"); } return new LoopingIterator(coll); } /** * Gets an iterator that loops continuously over the supplied list. * <p> * The iterator will only stop looping if the remove method is called * enough times to empty the list, or if the list is empty to start with. * * @param list the list to iterate over, not null * @return a new looping iterator * @throws NullPointerException if the list is null */ public static ResettableIterator loopingListIterator(List list) { if (list == null) { throw new NullPointerException("List must not be null"); } return new LoopingListIterator(list); } // Views //----------------------------------------------------------------------- /** * Gets an iterator that provides an iterator view of the given enumeration. * * @param enumeration the enumeration to use * @return a new iterator */ public static Iterator asIterator(Enumeration enumeration) { if (enumeration == null) { throw new NullPointerException("Enumeration must not be null"); } return new EnumerationIterator(enumeration); } /** * Gets an iterator that provides an iterator view of the given enumeration * that will remove elements from the specified collection. * * @param enumeration the enumeration to use * @param removeCollection the collection to remove elements from * @return a new iterator */ public static Iterator asIterator(Enumeration enumeration, Collection removeCollection) { if (enumeration == null) { throw new NullPointerException("Enumeration must not be null"); } if (removeCollection == null) { throw new NullPointerException("Collection must not be null"); } return new EnumerationIterator(enumeration, removeCollection); } /** * Gets an enumeration that wraps an iterator. * * @param iterator the iterator to use, not null * @return a new enumeration * @throws NullPointerException if iterator is null */ public static Enumeration asEnumeration(Iterator iterator) { if (iterator == null) { throw new NullPointerException("Iterator must not be null"); } return new IteratorEnumeration(iterator); } /** * Gets a list iterator based on a simple iterator. * <p> * As the wrapped Iterator is traversed, a LinkedList of its values is * cached, permitting all required operations of ListIterator. * * @param iterator the iterator to use, not null * @return a new iterator * @throws NullPointerException if iterator parameter is null */ public static ListIterator toListIterator(Iterator iterator) { if (iterator == null) { throw new NullPointerException("Iterator must not be null"); } return new ListIteratorWrapper(iterator); } /** * Gets an array based on an iterator. * <p> * As the wrapped Iterator is traversed, an ArrayList of its values is * created. At the end, this is converted to an array. * * @param iterator the iterator to use, not null * @return an array of the iterator contents * @throws NullPointerException if iterator parameter is null */ public static Object[] toArray(Iterator iterator) { if (iterator == null) { throw new NullPointerException("Iterator must not be null"); } List list = toList(iterator, 100); return list.toArray(); } /** * Gets an array based on an iterator. * <p> * As the wrapped Iterator is traversed, an ArrayList of its values is * created. At the end, this is converted to an array. * * @param iterator the iterator to use, not null * @param arrayClass the class of array to create * @return an array of the iterator contents * @throws NullPointerException if iterator parameter is null * @throws NullPointerException if arrayClass is null * @throws ClassCastException if the arrayClass is invalid */ public static Object[] toArray(Iterator iterator, Class arrayClass) { if (iterator == null) { throw new NullPointerException("Iterator must not be null"); } if (arrayClass == null) { throw new NullPointerException("Array class must not be null"); } List list = toList(iterator, 100); return list.toArray((Object[]) Array.newInstance(arrayClass, list.size())); } /** * Gets a list based on an iterator. * <p> * As the wrapped Iterator is traversed, an ArrayList of its values is * created. At the end, the list is returned. * * @param iterator the iterator to use, not null * @return a list of the iterator contents * @throws NullPointerException if iterator parameter is null */ public static List toList(Iterator iterator) { return toList(iterator, 10); } /** * Gets a list based on an iterator. * <p> * As the wrapped Iterator is traversed, an ArrayList of its values is * created. At the end, the list is returned. * * @param iterator the iterator to use, not null * @param estimatedSize the initial size of the ArrayList * @return a list of the iterator contents * @throws NullPointerException if iterator parameter is null * @throws IllegalArgumentException if the size is less than 1 */ public static List toList(Iterator iterator, int estimatedSize) { if (iterator == null) { throw new NullPointerException("Iterator must not be null"); } if (estimatedSize < 1) { throw new IllegalArgumentException("Estimated size must be greater than 0"); } List list = new ArrayList(estimatedSize); while (iterator.hasNext()) { list.add(iterator.next()); } return list; } /** * Gets a suitable Iterator for the given object. * <p> * This method can handles objects as follows * <ul> * <li>null - empty iterator * <li>Iterator - returned directly * <li>Enumeration - wrapped * <li>Collection - iterator from collection returned * <li>Map - values iterator returned * <li>Dictionary - values (elements) enumeration returned as iterator * <li>array - iterator over array returned * <li>object with iterator() public method accessed by reflection * <li>object - singleton iterator * </ul> * * @param obj the object to convert to an iterator * @return a suitable iterator, never null */ public static Iterator getIterator(Object obj) { if (obj == null) { return emptyIterator(); } else if (obj instanceof Iterator) { return (Iterator) obj; } else if (obj instanceof Collection) { return ((Collection) obj).iterator(); } else if (obj instanceof Object[]) { return new ObjectArrayIterator((Object[]) obj); } else if (obj instanceof Enumeration) { return new EnumerationIterator((Enumeration) obj); } else if (obj instanceof Map) { return ((Map) obj).values().iterator(); } else if (obj instanceof Dictionary) { return new EnumerationIterator(((Dictionary) obj).elements()); } else if (obj != null && obj.getClass().isArray()) { return new ArrayIterator(obj); } else { try { Method method = obj.getClass().getMethod("iterator", null); if (Iterator.class.isAssignableFrom(method.getReturnType())) { Iterator it = (Iterator) method.invoke(obj, null); if (it != null) { return it; } } } catch (Exception ex) { // ignore } return singletonIterator(obj); } } }