- /*
- * 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.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.
- * <p>
- * Given two ordered {@link Iterator} instances <code>A</code> and <code>B</code>,
- * the {@link #next} method on this iterator will return the lesser of
- * <code>A.next()</code> and <code>B.next()</code>.
- *
- * @since Commons Collections 2.1
- * @version $Revision: 1.13 $ $Date: 2004/02/18 00:59:50 $
- *
- * @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 <code>CollatingIterator</code>. 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 <code>CollatingIterator</code> 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 <code>CollatingIterator</code> 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 <code>CollatingIterator</code> 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 <code>CollatingIterator</code> 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 <code>CollatingIterator</code> 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 <code>true</code> 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>i</i> to the next value of the
- * {@link #iterators iterator} at position <i>i</i>, or
- * clear them if the <i>i</i><sup>th</sup> iterator
- * has no next value.
- *
- * @return <tt>false</tt> 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>i</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 <code>true</code> iff any bit in the given set is
- * <code>true</code>.
- */
- private boolean anyValueSet(BitSet set) {
- for (int i = 0; i < set.size(); i++) {
- if (set.get(i)) {
- return true;
- }
- }
- return false;
- }
-
- /**
- * Returns <code>true</code> 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;
- }
-
- }