/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.iterators;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import org.apache.commons.collections.ResettableListIterator;
/**
* Converts an iterator into a list iterator by caching the returned entries.
* <p>
* The <code>ListIterator</code> interface has additional useful methods
* for navigation - <code>previous()</code> and the index methods.
* This class allows a regular <code>Iterator</code> to behave as a
* <code>ListIterator</code>. It achieves this by building a list internally
* of as the underlying iterator is traversed.
* <p>
* The optional operations of <code>ListIterator</code> are not supported.
* <p>
* This class implements ResettableListIterator from Commons Collections 3.2.
*
* @since Commons Collections 2.1
* @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
*
* @author Morgan Delagrange
* @author Stephen Colebourne
*/
public class ListIteratorWrapper implements ResettableListIterator {
/** Message used when remove, set or add are called. */
private static final String UNSUPPORTED_OPERATION_MESSAGE =
"ListIteratorWrapper does not support optional operations of ListIterator.";
/** The underlying iterator being decorated. */
private final Iterator iterator;
/** The list being used to cache the iterator. */
private final List list = new ArrayList();
/** The current index of this iterator. */
private int currentIndex = 0;
/** The current index of the wrapped iterator. */
private int wrappedIteratorIndex = 0;
// Constructor
//-------------------------------------------------------------------------
/**
* Constructs a new <code>ListIteratorWrapper</code> that will wrap
* the given iterator.
*
* @param iterator the iterator to wrap
* @throws NullPointerException if the iterator is null
*/
public ListIteratorWrapper(Iterator iterator) {
super();
if (iterator == null) {
throw new NullPointerException("Iterator must not be null");
}
this.iterator = iterator;
}
// ListIterator interface
//-------------------------------------------------------------------------
/**
* Throws {@link UnsupportedOperationException}.
*
* @param obj the object to add, ignored
* @throws UnsupportedOperationException always
*/
public void add(Object obj) throws UnsupportedOperationException {
throw new UnsupportedOperationException(UNSUPPORTED_OPERATION_MESSAGE);
}
/**
* Returns true if there are more elements in the iterator.
*
* @return true if there are more elements
*/
public boolean hasNext() {
if (currentIndex == wrappedIteratorIndex) {
return iterator.hasNext();
}
return true;
}
/**
* Returns true if there are previous elements in the iterator.
*
* @return true if there are previous elements
*/
public boolean hasPrevious() {
if (currentIndex == 0) {
return false;
}
return true;
}
/**
* Returns the next element from the iterator.
*
* @return the next element from the iterator
* @throws NoSuchElementException if there are no more elements
*/
public Object next() throws NoSuchElementException {
if (currentIndex < wrappedIteratorIndex) {
++currentIndex;
return list.get(currentIndex - 1);
}
Object retval = iterator.next();
list.add(retval);
++currentIndex;
++wrappedIteratorIndex;
return retval;
}
/**
* Returns in the index of the next element.
*
* @return the index of the next element
*/
public int nextIndex() {
return currentIndex;
}
/**
* Returns the the previous element.
*
* @return the previous element
* @throws NoSuchElementException if there are no previous elements
*/
public Object previous() throws NoSuchElementException {
if (currentIndex == 0) {
throw new NoSuchElementException();
}
--currentIndex;
return list.get(currentIndex);
}
/**
* Returns the index of the previous element.
*
* @return the index of the previous element
*/
public int previousIndex() {
return currentIndex - 1;
}
/**
* Throws {@link UnsupportedOperationException}.
*
* @throws UnsupportedOperationException always
*/
public void remove() throws UnsupportedOperationException {
throw new UnsupportedOperationException(UNSUPPORTED_OPERATION_MESSAGE);
}
/**
* Throws {@link UnsupportedOperationException}.
*
* @param obj the object to set, ignored
* @throws UnsupportedOperationException always
*/
public void set(Object obj) throws UnsupportedOperationException {
throw new UnsupportedOperationException(UNSUPPORTED_OPERATION_MESSAGE);
}
// ResettableIterator interface
//-------------------------------------------------------------------------
/**
* Resets this iterator back to the position at which the iterator
* was created.
*
* @since Commons Collections 3.2
*/
public void reset() {
currentIndex = 0;
}
}