org.eclipse.rdf4j.common.iteration.ConvertingIteration 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;

/**
 * A CloseableIteration that converts an iteration over objects of type S (the source type) to an
 * iteration over objects of type T (the target type).
 */
public abstract class ConvertingIteration
		extends AbstractCloseableIteration
{

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

	/**
	 * The source type iteration.
	 */
	private final Iteration iter;

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

	/**
	 * Creates a new ConvertingIteration that operates on the supplied source type iteration.
	 * 
	 * @param iter
	 *        The source type iteration for this ConvertingIteration, must not be null.
	 */
	public ConvertingIteration(Iteration iter) {
		assert iter != null;
		this.iter = iter;
	}

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

	/**
	 * Converts a source type object to a target type object.
	 */
	protected abstract T convert(S sourceObject)
		throws X;

	/**
	 * Checks whether the source type iteration contains more elements.
	 * 
	 * @return true if the source type iteration contains more elements, false otherwise.
	 * @throws X
	 */
	public boolean hasNext()
		throws X
	{
		return iter.hasNext();
	}

	/**
	 * Returns the next element from the source type iteration.
	 * 
	 * @throws X
	 * @throws java.util.NoSuchElementException
	 *         If all elements have been returned.
	 * @throws IllegalStateException
	 *         If the iteration has been closed.
	 */
	public T next()
		throws X
	{
		return convert(iter.next());
	}

	/**
	 * Calls remove() on the underlying Iteration.
	 * 
	 * @throws UnsupportedOperationException
	 *         If the wrapped Iteration does not support the remove operation.
	 * @throws IllegalStateException
	 *         If the Iteration has been closed, or if {@link #next} has not yet been called, or
	 *         {@link #remove} has already been called after the last call to {@link #next}.
	 */
	public void remove()
		throws X
	{
		iter.remove();
	}

	/**
	 * Closes this iteration as well as the wrapped iteration if it is a {@link CloseableIteration}.
	 */
	@Override
	protected void handleClose()
		throws X
	{
		super.handleClose();
		Iterations.closeCloseable(iter);
	}
}