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Posted to dev@commons.apache.org by sc...@apache.org on 2002/08/17 13:38:53 UTC
cvs commit: jakarta-commons/collections/src/java/org/apache/commons/collections IteratorUtils.java
scolebourne 2002/08/17 04:38:53
Added: collections/src/java/org/apache/commons/collections
IteratorUtils.java
Log:
Initial checkin
Revision Changes Path
1.1 jakarta-commons/collections/src/java/org/apache/commons/collections/IteratorUtils.java
Index: IteratorUtils.java
===================================================================
/*
* $Header: /home/cvs/jakarta-commons/collections/src/java/org/apache/commons/collections/IteratorUtils.java,v 1.1 2002/08/17 11:38:53 scolebourne Exp $
* $Revision: 1.1 $
* $Date: 2002/08/17 11:38:53 $
*
* ====================================================================
*
* The Apache Software License, Version 1.1
*
* Copyright (c) 1999-2001 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowlegement:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements normally appear.
*
* 4. The names "The Jakarta Project", "Commons", and "Apache Software
* Foundation" must not be used to endorse or promote products derived
* from this software without prior written permission. For written
* permission, please contact apache@apache.org.
*
* 5. Products derived from this software may not be called "Apache"
* nor may "Apache" appear in their names without prior written
* permission of the Apache Group.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*
*/
package org.apache.commons.collections;
import java.lang.reflect.Method;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Dictionary;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.ListIterator;
import java.util.Map;
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 1.1 2002/08/17 11:38:53 scolebourne Exp $
* @since 2.1
*/
public class IteratorUtils {
// validation is done in this class in certain cases because the
// public classes allow invalid states
/**
* 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
*/
public static Iterator emptyIterator() {
return Collections.EMPTY_LIST.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
*/
public static ListIterator emptyListIterator() {
return Collections.EMPTY_LIST.listIterator();
}
/**
* 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
*/
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
*/
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
*/
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
*/
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 #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 #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 #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 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 Iterator iteratorListIterator(Iterator iterator) {
return new ListIteratorWrapper(iterator);
}
/**
* Gets an iterator that provides an iterator view of the given enumeration.
*
* @param enumeration the enumeration to use
*/
public static Iterator enumerationIterator(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 enumerationIterator(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 iteratorEnumeration(Iterator iterator) {
if (iterator == null) {
throw new NullPointerException("Iterator must not be null");
}
return new IteratorEnumeration(iterator);
}
/**
* 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);
}
}
}
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