001/*
002 * ModeShape (http://www.modeshape.org)
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *       http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.modeshape.common.collection;
018
019import java.util.Iterator;
020import java.util.NoSuchElementException;
021import org.modeshape.common.annotation.NotThreadSafe;
022
023/**
024 * An iterator implementation that wraps multiple other iterators.
025 *
026 * @author Randall Hauch (rhauch@redhat.com)
027 * @param <E> the value type
028 */
029@NotThreadSafe
030public final class MultiIterator<E> implements Iterator<E> {
031
032    public static <E> MultiIterator<E> fromIterators( Iterable<Iterator<E>> iterators ) {
033        return new MultiIterator<>(iterators);
034    }
035
036    public static <E> MultiIterator<E> fromIterables( final Iterable<? extends Iterable<E>> iterables ) {
037        final Iterator<? extends Iterable<E>> iterator = iterables.iterator();
038        Iterable<Iterator<E>> iterators = new Iterable<Iterator<E>>() {
039            @Override
040            public Iterator<Iterator<E>> iterator() {
041                return new Iterator<Iterator<E>>() {
042                    @Override
043                    public boolean hasNext() {
044                        return iterator.hasNext();
045                    }
046
047                    @Override
048                    public Iterator<E> next() {
049                        return iterator.next().iterator();
050                    }
051
052                    @Override
053                    public void remove() {
054                        iterator.remove();
055                    }
056                };
057            }
058        };
059        return new MultiIterator<>(iterators);
060    }
061
062    private final Iterator<Iterator<E>> iterators;
063    private Iterator<E> current;
064
065    protected MultiIterator( Iterable<Iterator<E>> iterators ) {
066        this.iterators = iterators.iterator();
067    }
068
069    @Override
070    public boolean hasNext() {
071        if (nextIterator()) return current.hasNext();
072        return false;
073    }
074
075    @Override
076    public E next() {
077        if (nextIterator()) return current.next();
078        throw new NoSuchElementException();
079    }
080
081    protected boolean nextIterator() {
082        while (current == null || !current.hasNext()) {
083            // Find the next iterator ...
084            if (!iterators.hasNext()) return false;
085            current = iterators.next();
086        }
087        return true;
088    }
089
090    @Override
091    public void remove() {
092        throw new UnsupportedOperationException();
093    }
094
095}