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A module of the Hibernate Core project
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/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as
 * indicated by the @author tags or express copyright attribution
 * statements applied by the authors.  All third-party contributions are
 * distributed under license by Red Hat Middleware LLC.
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 *
 */
package org.hibernate.internal.util.collections;

import java.util.Iterator;
import java.util.List;

/**
 * An JoinedIterator 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 JoinedIterator
 * will delegate to a single underlying Iterator. The JoinedIterator will
 * invoke the Iterators in sequence until all Iterators are exhausted.
 *
 */
public class JoinedIterator implements Iterator {

	private static final Iterator[] ITERATORS = {};

	// wrapped iterators
	private Iterator[] iterators;

	// index of current iterator in the wrapped iterators array
	private int currentIteratorIndex;

	// the current iterator
	private Iterator currentIterator;

	// the last used iterator
	private Iterator lastUsedIterator;

	public JoinedIterator(List iterators) {
		this( (Iterator[]) iterators.toArray(ITERATORS) );
	}

	public JoinedIterator(Iterator[] iterators) {
		if( iterators==null )
			throw new NullPointerException("Unexpected NULL iterators argument");
		this.iterators = iterators;
	}

	public JoinedIterator(Iterator first, Iterator second) {
		this( new Iterator[] { first, second } );
	}

	public boolean hasNext() {
		updateCurrentIterator();
		return currentIterator.hasNext();
	}

	public Object next() {
		updateCurrentIterator();
		return currentIterator.next();
	}

	public void remove() {
		updateCurrentIterator();
		lastUsedIterator.remove();
	}


	// call this before any Iterator method to make sure that the current Iterator
	// is not exhausted
	protected void updateCurrentIterator() {

		if (currentIterator == null) {
			if( iterators.length==0  ) {
				currentIterator = EmptyIterator.INSTANCE;
			}
			else {
				currentIterator = iterators[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() && currentIteratorIndex < iterators.length - 1) {
			currentIteratorIndex++;
			currentIterator = iterators[currentIteratorIndex];
		}
	}

}