/*
* Copyright 1999-2004 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 java.util.NoSuchElementException;
import org.apache.commons.collections.iterators.ArrayIterator;
import org.apache.commons.collections.iterators.CollatingIterator;
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.SingletonIterator;
import org.apache.commons.collections.iterators.SingletonListIterator;
import org.apache.commons.collections.iterators.TransformIterator;
/**
* Provides static utility methods and decorators for {@link Iterator}
* instances. The implementations are provided in the
* <code>org.apache.commons.collections.iterators</code> subpackage.
*
* @author <a href="mailto:scolebourne@joda.org">Stephen Colebourne</a>
* @version $Id: IteratorUtils.java,v 1.4.2.2 2004/05/22 12:14:01 scolebourne Exp $
* @since 2.1
*/
public class IteratorUtils {
// validation is done in this class in certain cases because the
// public classes allow invalid states
/**
* An iterator over no elements.
* @deprecated Use <code>EmptyIterator.INSTANCE</code>
*/
public static final Iterator EMPTY_ITERATOR = new EmptyIterator();
/**
* A list iterator over no elements
* @deprecated Use <code>EmptyListIterator.INSTANCE</code>
*/
public static final ListIterator EMPTY_LIST_ITERATOR = new EmptyListIterator();
/**
* Prevents instantiation.
*/
private IteratorUtils() {
}
/**
* Gets an empty iterator.
* <p>
* This iterator is a valid iterator object that will iterate over
* nothing.
*
* @return an iterator over nothing
* @deprecated Use <code>EmptyIterator.INSTANCE</code>
*/
public static Iterator emptyIterator() {
return EMPTY_ITERATOR;
}
/**
* Gets an empty list iterator.
* <p>
* This iterator is a valid list iterator object that will iterate
* over nothing.
*
* @return a list iterator over nothing
* @deprecated Use <code>EmptyListIterator.INSTANCE</code>
*/
public static ListIterator emptyListIterator() {
return EMPTY_LIST_ITERATOR;
}
/**
* Gets a singleton iterator.
* <p>
* This iterator is a valid iterator object that will iterate over
* the specified object.
*
* @param object the single object over which to iterate
* @return a singleton iterator over the object
* @deprecated Use <code>new SingletonIterator(object)</code>
*/
public static Iterator 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);
}
/**
* Gets an iterator over an array.
*
* @param array the array over which to iterate
* @return an iterator over the array
* @throws NullPointerException if array is null
* @deprecated Use <code>new ArrayIterator(array)</code>
*/
public static Iterator arrayIterator(Object[] array) {
return new ArrayIterator(array);
}
/**
* Gets an iterator over the end part of an array.
*
* @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 array bounds are invalid
* @throws NullPointerException if array is null
* @deprecated Use <code>new ArrayIterator(array,start)</code>
*/
public static Iterator arrayIterator(Object[] array, int start) {
return new ArrayIterator(array, start);
}
/**
* Gets an iterator over part of an 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 an iterator over part of the array
* @throws IllegalArgumentException if array bounds are invalid
* @throws NullPointerException if array is null
* @deprecated Use <code>new ArrayIterator(array,start,end)</code>
*/
public static Iterator arrayIterator(Object[] array, int start, int end) {
return new ArrayIterator(array, start, end);
}
// /**
// * Gets a list iterator over an array.
// *
// * @param array the array over which to iterate
// * @return a list iterator over the array
// * @throws NullPointerException if array is null
// */
// public static ListIterator arrayListIterator(Object[] array) {
// return new ArrayListIterator(array);
// }
//
// /**
// * Gets a list iterator over the end part of an 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 IllegalArgumentException if array bounds are invalid
// * @throws NullPointerException if array is null
// */
// public static ListIterator arrayListIterator(Object[] array, int start) {
// return new ArrayListIterator(array, start);
// }
//
// /**
// * Gets a list iterator over part of an 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 IllegalArgumentException if array bounds are invalid
// * @throws NullPointerException if array is null
// */
// public static ListIterator arrayListIterator(Object[] array, int start, int end) {
// return new ArrayListIterator(array, start, end);
// }
/**
* 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);
}
/**
* 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);
}
/**
* 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
* @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);
}
/**
* 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
* @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
* @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);
}
/**
* Gets an iterator that provides an iterator view of the given enumeration.
*
* @param enumeration the enumeration to use
*/
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 collection the collection to remove elements form
*/
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
* @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
* @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
* @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
* @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
* @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
* @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 ArrayIterator(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);
}
}
/**
* EmptyIterator class
*/
static class EmptyIterator implements Iterator {
/**
* @see java.util.Iterator#hasNext()
*/
public boolean hasNext() {
return false;
}
/**
* @see java.util.Iterator#next()
*/
public Object next() {
throw new NoSuchElementException();
}
/**
* @see java.util.Iterator#remove()
*/
public void remove() {
throw new UnsupportedOperationException("remove() not supported for empty Iterator");
}
}
/**
* EmptyListIterator class
*/
static class EmptyListIterator extends EmptyIterator implements ListIterator {
/**
* @see java.util.ListIterator#hasPrevious()
*/
public boolean hasPrevious() {
return false;
}
/**
* @see java.util.ListIterator#previous()
*/
public Object previous() {
throw new NoSuchElementException();
}
/**
* @see java.util.ListIterator#nextIndex()
*/
public int nextIndex() {
return 0;
}
/**
* @see java.util.ListIterator#previousIndex()
*/
public int previousIndex() {
return -1;
}
/**
* @see java.util.ListIterator#add(Object)
*/
public void add(Object o) {
throw new UnsupportedOperationException("add() not supported for empty Iterator");
}
/**
* @see java.util.ListIterator#set(Object)
*/
public void set(Object o) {
throw new UnsupportedOperationException("set() not supported for empty Iterator");
}
}
}