ZipIterator.java

/*
 * Copyright (c) 2013, SRI International
 * All rights reserved.
 * Licensed under the The BSD 3-Clause License;
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 * 
 * http://opensource.org/licenses/BSD-3-Clause
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * 
 * Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 * 
 * Neither the name of the aic-util nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package com.sri.ai.util.collect;

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

import com.google.common.annotations.Beta;


/**
 * A ZipIterator is constructed on an array of iterators, and iterates over
 * lists of their next elements until one of them runs out of elements. For
 * example, if given iterators for collections (1,2,3), (a, b, c) and (x, y), it
 * will range over lists (1,a,x) and (2,b,y).
 * 
 * @author braz
 */
@Beta
public class ZipIterator extends EZIteratorWithNull<List<Object>> {

	Iterator<?>[] iterators;

	public ZipIterator(Iterator<?>... iterators) {
		this.iterators = iterators;
	}

	public ZipIterator(List<Iterator<?>> iterators) {
		this.iterators = iterators.toArray(new Iterator[iterators.size()]);
	}

	@Override
	protected List<Object> calculateNext() {
		List<Object> next = new LinkedList<Object>();
		for (Iterator<?> iterator : iterators) {
			if (iterator.hasNext()) {
				Object nextFromIterator = iterator.next();
				next.add(nextFromIterator);
			} 
			else {
				endOfRange();
				return null;
			}
		}
		return next;
	}
}