org.eclipse.rdf4j.common.iteration.LimitIteration Maven / Gradle / Ivy

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/*******************************************************************************
 * Copyright (c) 2015 Eclipse RDF4J contributors, Aduna, and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Distribution License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *******************************************************************************/

package org.eclipse.rdf4j.common.iteration;

import java.util.NoSuchElementException;

/**
 * An Iteration that limits the amount of elements that it returns from an underlying Iteration to a fixed
 * amount. This class returns the first limit elements from the underlying Iteration and drops the
 * rest.
 */
public class LimitIteration extends IterationWrapper {

	/*-----------*
	 * Variables *
	 *-----------*/

	/**
	 * The amount of elements to return.
	 */
	private final long limit;

	/**
	 * The number of elements that have been returned so far.
	 */
	private long returnCount;

	/*--------------*
	 * Constructors *
	 *--------------*/

	/**
	 * Creates a new LimitIteration.
	 * 
	 * @param iter
	 *        The underlying Iteration, must not be null.
	 * @param limit
	 *        The number of query answers to return, must be >= 0.
	 */
	public LimitIteration(Iteration iter, long limit) {
		super(iter);

		assert iter != null;
		assert limit >= 0;

		this.limit = limit;
		this.returnCount = 0;
	}

	/*---------*
	 * Methods *
	 *---------*/

	@Override
	public boolean hasNext()
		throws X
	{
		return returnCount < limit && super.hasNext();
	}

	@Override
	public E next()
		throws X
	{
		if (returnCount >= limit) {
			throw new NoSuchElementException("limit reached");
		}

		returnCount++;
		return super.next();
	}
}