org.apache.commons.collections.iterators.IteratorChain Maven / Gradle / Ivy
/*
* 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.Collection;
import java.util.Iterator;
import java.util.List;
import org.apache.commons.collections.list.UnmodifiableList;
/**
* An IteratorChain is an Iterator that wraps a number of Iterators.
*
* This class makes multiple iterators look like one to the caller
* When any method from the Iterator interface is called, the IteratorChain
* will delegate to a single underlying Iterator. The IteratorChain will
* invoke the Iterators in sequence until all Iterators are exhausted.
*
* Under many circumstances, linking Iterators together in this manner is
* more efficient (and convenient) than reading out the contents of each
* Iterator into a List and creating a new Iterator.
*
* Calling a method that adds new Iteratorafter a method in the Iterator
* interface has been called will result in an UnsupportedOperationException.
* Subclasses should take care to not alter the underlying List of Iterators.
*
* NOTE: As from version 3.0, the IteratorChain may contain no
* iterators. In this case the class will function as an empty iterator.
*
* @since Commons Collections 2.1
* @version $Revision: 647116 $ $Date: 2008-04-11 12:23:08 +0100 (Fri, 11 Apr 2008) $
*
* @author Morgan Delagrange
* @author Stephen Colebourne
*/
public class IteratorChain implements Iterator {
/** The chain of iterators */
protected final List iteratorChain = new ArrayList();
/** The index of the current iterator */
protected int currentIteratorIndex = 0;
/** The current iterator */
protected Iterator currentIterator = null;
/**
* The "last used" Iterator is the Iterator upon which
* next() or hasNext() was most recently called
* used for the remove() operation only
*/
protected Iterator lastUsedIterator = null;
/**
* ComparatorChain is "locked" after the first time
* compare(Object,Object) is called
*/
protected boolean isLocked = false;
//-----------------------------------------------------------------------
/**
* Construct an IteratorChain with no Iterators.
*
* You will normally use {@link #addIterator(Iterator)} to add
* some iterators after using this constructor.
*/
public IteratorChain() {
super();
}
/**
* Construct an IteratorChain with a single Iterator.
*
* @param iterator first Iterator in the IteratorChain
* @throws NullPointerException if the iterator is null
*/
public IteratorChain(Iterator iterator) {
super();
addIterator(iterator);
}
/**
* Constructs a new IteratorChain over the two
* given iterators.
*
* @param a the first child iterator
* @param b the second child iterator
* @throws NullPointerException if either iterator is null
*/
public IteratorChain(Iterator a, Iterator b) {
super();
addIterator(a);
addIterator(b);
}
/**
* Constructs a new IteratorChain over the array
* of iterators.
*
* @param iterators the array of iterators
* @throws NullPointerException if iterators array is or contains null
*/
public IteratorChain(Iterator[] iterators) {
super();
for (int i = 0; i < iterators.length; i++) {
addIterator(iterators[i]);
}
}
/**
* Constructs a new IteratorChain over the collection
* of iterators.
*
* @param iterators the collection of iterators
* @throws NullPointerException if iterators collection is or contains null
* @throws ClassCastException if iterators collection doesn't contain an iterator
*/
public IteratorChain(Collection iterators) {
super();
for (Iterator it = iterators.iterator(); it.hasNext();) {
Iterator item = (Iterator) it.next();
addIterator(item);
}
}
//-----------------------------------------------------------------------
/**
* Add an Iterator to the end of the chain
*
* @param iterator Iterator to add
* @throws IllegalStateException if I've already started iterating
* @throws NullPointerException if the iterator is null
*/
public void addIterator(Iterator iterator) {
checkLocked();
if (iterator == null) {
throw new NullPointerException("Iterator must not be null");
}
iteratorChain.add(iterator);
}
/**
* Set the Iterator at the given index
*
* @param index index of the Iterator to replace
* @param iterator Iterator to place at the given index
* @throws IndexOutOfBoundsException if index < 0 or index > size()
* @throws IllegalStateException if I've already started iterating
* @throws NullPointerException if the iterator is null
*/
public void setIterator(int index, Iterator iterator) throws IndexOutOfBoundsException {
checkLocked();
if (iterator == null) {
throw new NullPointerException("Iterator must not be null");
}
iteratorChain.set(index, iterator);
}
/**
* Get the list of Iterators (unmodifiable)
*
* @return the unmodifiable list of iterators added
*/
public List getIterators() {
return UnmodifiableList.decorate(iteratorChain);
}
/**
* Number of Iterators in the current IteratorChain.
*
* @return Iterator count
*/
public int size() {
return iteratorChain.size();
}
/**
* Determine if modifications can still be made to the IteratorChain.
* IteratorChains cannot be modified once they have executed a method
* from the Iterator interface.
*
* @return true if IteratorChain cannot be modified, false if it can
*/
public boolean isLocked() {
return isLocked;
}
/**
* Checks whether the iterator chain is now locked and in use.
*/
private void checkLocked() {
if (isLocked == true) {
throw new UnsupportedOperationException("IteratorChain cannot be changed after the first use of a method from the Iterator interface");
}
}
/**
* Lock the chain so no more iterators can be added.
* This must be called from all Iterator interface methods.
*/
private void lockChain() {
if (isLocked == false) {
isLocked = true;
}
}
/**
* Updates the current iterator field to ensure that the current Iterator
* is not exhausted
*/
protected void updateCurrentIterator() {
if (currentIterator == null) {
if (iteratorChain.isEmpty()) {
currentIterator = EmptyIterator.INSTANCE;
} else {
currentIterator = (Iterator) iteratorChain.get(0);
}
// set last used iterator here, in case the user calls remove
// before calling hasNext() or next() (although they shouldn't)
lastUsedIterator = currentIterator;
}
while (currentIterator.hasNext() == false && currentIteratorIndex < iteratorChain.size() - 1) {
currentIteratorIndex++;
currentIterator = (Iterator) iteratorChain.get(currentIteratorIndex);
}
}
//-----------------------------------------------------------------------
/**
* Return true if any Iterator in the IteratorChain has a remaining element.
*
* @return true if elements remain
*/
public boolean hasNext() {
lockChain();
updateCurrentIterator();
lastUsedIterator = currentIterator;
return currentIterator.hasNext();
}
/**
* Returns the next Object of the current Iterator
*
* @return Object from the current Iterator
* @throws java.util.NoSuchElementException if all the Iterators are exhausted
*/
public Object next() {
lockChain();
updateCurrentIterator();
lastUsedIterator = currentIterator;
return currentIterator.next();
}
/**
* Removes from the underlying collection the last element
* returned by the Iterator. As with next() and hasNext(),
* this method calls remove() on the underlying Iterator.
* Therefore, this method may throw an
* UnsupportedOperationException if the underlying
* Iterator does not support this method.
*
* @throws UnsupportedOperationException
* if the remove operator is not supported by the underlying Iterator
* @throws IllegalStateException
* if the next method has not yet been called, or the remove method has
* already been called after the last call to the next method.
*/
public void remove() {
lockChain();
if (currentIterator == null) {
updateCurrentIterator();
}
lastUsedIterator.remove();
}
}