org.apache.commons.collections.iterators.CollatingIterator 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.BitSet;
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import org.apache.commons.collections.list.UnmodifiableList;
/**
* Provides an ordered iteration over the elements contained in
* a collection of ordered Iterators.
*
* Given two ordered {@link Iterator} instances A and B,
* the {@link #next} method on this iterator will return the lesser of
* A.next() and B.next().
*
* @since Commons Collections 2.1
* @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
*
* @author Rodney Waldhoff
* @author Stephen Colebourne
*/
public class CollatingIterator implements Iterator {
/** The {@link Comparator} used to evaluate order. */
private Comparator comparator = null;
/** The list of {@link Iterator}s to evaluate. */
private ArrayList iterators = null;
/** {@link Iterator#next Next} objects peeked from each iterator. */
private ArrayList values = null;
/** Whether or not each {@link #values} element has been set. */
private BitSet valueSet = null;
/** Index of the {@link #iterators iterator} from whom the last returned value was obtained. */
private int lastReturned = -1;
// Constructors
// ----------------------------------------------------------------------
/**
* Constructs a new CollatingIterator. Natural sort order
* will be used, and child iterators will have to be manually added
* using the {@link #addIterator(Iterator)} method.
*/
public CollatingIterator() {
this(null,2);
}
/**
* Constructs a new CollatingIterator that will used the
* specified comparator for ordering. Child iterators will have to be
* manually added using the {@link #addIterator(Iterator)} method.
*
* @param comp the comparator to use to sort, or null to use natural sort order
*/
public CollatingIterator(final Comparator comp) {
this(comp,2);
}
/**
* Constructs a new CollatingIterator that will used the
* specified comparator for ordering and have the specified initial
* capacity. Child iterators will have to be
* manually added using the {@link #addIterator(Iterator)} method.
*
* @param comp the comparator to use to sort, or null to use natural sort order
* @param initIterCapacity the initial capacity for the internal list
* of child iterators
*/
public CollatingIterator(final Comparator comp, final int initIterCapacity) {
iterators = new ArrayList(initIterCapacity);
setComparator(comp);
}
/**
* Constructs a new CollatingIterator that will use the
* specified comparator to provide ordered iteration over the two
* given iterators.
*
* @param comp the comparator to use to sort, or null to use natural sort order
* @param a the first child ordered iterator
* @param b the second child ordered iterator
* @throws NullPointerException if either iterator is null
*/
public CollatingIterator(final Comparator comp, final Iterator a, final Iterator b) {
this(comp,2);
addIterator(a);
addIterator(b);
}
/**
* Constructs a new CollatingIterator that will use the
* specified comparator to provide ordered iteration over the array
* of iterators.
*
* @param comp the comparator to use to sort, or null to use natural sort order
* @param iterators the array of iterators
* @throws NullPointerException if iterators array is or contains null
*/
public CollatingIterator(final Comparator comp, final Iterator[] iterators) {
this(comp, iterators.length);
for (int i = 0; i < iterators.length; i++) {
addIterator(iterators[i]);
}
}
/**
* Constructs a new CollatingIterator that will use the
* specified comparator to provide ordered iteration over the collection
* of iterators.
*
* @param comp the comparator to use to sort, or null to use natural sort order
* @param iterators the collection of iterators
* @throws NullPointerException if the iterators collection is or contains null
* @throws ClassCastException if the iterators collection contains an
* element that's not an {@link Iterator}
*/
public CollatingIterator(final Comparator comp, final Collection iterators) {
this(comp, iterators.size());
for (Iterator it = iterators.iterator(); it.hasNext();) {
Iterator item = (Iterator) it.next();
addIterator(item);
}
}
// Public Methods
// ----------------------------------------------------------------------
/**
* Adds the given {@link Iterator} to the iterators being collated.
*
* @param iterator the iterator to add to the collation, must not be null
* @throws IllegalStateException if iteration has started
* @throws NullPointerException if the iterator is null
*/
public void addIterator(final Iterator iterator) {
checkNotStarted();
if (iterator == null) {
throw new NullPointerException("Iterator must not be null");
}
iterators.add(iterator);
}
/**
* Sets 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 iteration has started
* @throws NullPointerException if the iterator is null
*/
public void setIterator(final int index, final Iterator iterator) {
checkNotStarted();
if (iterator == null) {
throw new NullPointerException("Iterator must not be null");
}
iterators.set(index, iterator);
}
/**
* Gets the list of Iterators (unmodifiable).
*
* @return the unmodifiable list of iterators added
*/
public List getIterators() {
return UnmodifiableList.decorate(iterators);
}
/**
* Gets the {@link Comparator} by which collatation occurs.
*/
public Comparator getComparator() {
return comparator;
}
/**
* Sets the {@link Comparator} by which collation occurs.
*
* @throws IllegalStateException if iteration has started
*/
public void setComparator(final Comparator comp) {
checkNotStarted();
comparator = comp;
}
// Iterator Methods
// -------------------------------------------------------------------
/**
* Returns true if any child iterator has remaining elements.
*
* @return true if this iterator has remaining elements
*/
public boolean hasNext() {
start();
return anyValueSet(valueSet) || anyHasNext(iterators);
}
/**
* Returns the next ordered element from a child iterator.
*
* @return the next ordered element
* @throws NoSuchElementException if no child iterator has any more elements
*/
public Object next() throws NoSuchElementException {
if (hasNext() == false) {
throw new NoSuchElementException();
}
int leastIndex = least();
if (leastIndex == -1) {
throw new NoSuchElementException();
} else {
Object val = values.get(leastIndex);
clear(leastIndex);
lastReturned = leastIndex;
return val;
}
}
/**
* Removes the last returned element from the child iterator that
* produced it.
*
* @throws IllegalStateException if there is no last returned element,
* or if the last returned element has already been removed
*/
public void remove() {
if (lastReturned == -1) {
throw new IllegalStateException("No value can be removed at present");
}
Iterator it = (Iterator) (iterators.get(lastReturned));
it.remove();
}
// Private Methods
// -------------------------------------------------------------------
/**
* Initializes the collating state if it hasn't been already.
*/
private void start() {
if (values == null) {
values = new ArrayList(iterators.size());
valueSet = new BitSet(iterators.size());
for (int i = 0; i < iterators.size(); i++) {
values.add(null);
valueSet.clear(i);
}
}
}
/**
* Sets the {@link #values} and {@link #valueSet} attributes
* at position i to the next value of the
* {@link #iterators iterator} at position i, or
* clear them if the ith iterator
* has no next value.
*
* @return false iff there was no value to set
*/
private boolean set(int i) {
Iterator it = (Iterator)(iterators.get(i));
if (it.hasNext()) {
values.set(i, it.next());
valueSet.set(i);
return true;
} else {
values.set(i,null);
valueSet.clear(i);
return false;
}
}
/**
* Clears the {@link #values} and {@link #valueSet} attributes
* at position i.
*/
private void clear(int i) {
values.set(i,null);
valueSet.clear(i);
}
/**
* Throws {@link IllegalStateException} if iteration has started
* via {@link #start}.
*
* @throws IllegalStateException if iteration started
*/
private void checkNotStarted() throws IllegalStateException {
if (values != null) {
throw new IllegalStateException("Can't do that after next or hasNext has been called.");
}
}
/**
* Returns the index of the least element in {@link #values},
* {@link #set(int) setting} any uninitialized values.
*
* @throws IllegalStateException
*/
private int least() {
int leastIndex = -1;
Object leastObject = null;
for (int i = 0; i < values.size(); i++) {
if (valueSet.get(i) == false) {
set(i);
}
if (valueSet.get(i)) {
if (leastIndex == -1) {
leastIndex = i;
leastObject = values.get(i);
} else {
Object curObject = values.get(i);
if (comparator.compare(curObject,leastObject) < 0) {
leastObject = curObject;
leastIndex = i;
}
}
}
}
return leastIndex;
}
/**
* Returns true iff any bit in the given set is
* true.
*/
private boolean anyValueSet(BitSet set) {
for (int i = 0; i < set.size(); i++) {
if (set.get(i)) {
return true;
}
}
return false;
}
/**
* Returns true iff any {@link Iterator}
* in the given list has a next value.
*/
private boolean anyHasNext(ArrayList iters) {
for (int i = 0; i < iters.size(); i++) {
Iterator it = (Iterator) iters.get(i);
if (it.hasNext()) {
return true;
}
}
return false;
}
}