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package org.aksw.commons.collections;


import java.util.Iterator;

/**
 * Created by Claus Stadler
 * Date: Oct 9, 2010
 * Time: 5:39:36 PM
 */
public abstract class PrefetchIterator
	implements Iterator
{
	//private static Logger logger = Logger.getLogger(PrefetchIterator.class);
	private Iterator	current		= null;
	private boolean		finished	= false;

	abstract protected Iterator prefetch()
		throws Exception;

	protected PrefetchIterator()
	{
	}

	private void preparePrefetch()
	{
		if (finished) {
			return;
		}

		current = null;
		try {
			// Prefetch may return empty iterators - skip them.
			do {
				current = prefetch();
			} while(current != null && !current.hasNext());
		}
		catch(Exception e) {
			//logger.error(ExceptionUtils.toString(e));
            e.printStackTrace();
		}
		if (current == null) {
            close();
			finished = true;
        }
	}

	private Iterator getCurrent()
	{
		if (current == null || !current.hasNext())
			preparePrefetch();

		return current;
	}

	public boolean hasNext()
	{
		return getCurrent() != null;
	}

	public T next()
	{
		return getCurrent().next();
	}

    public void close() {
        
    }

	public void remove()
	{
		throw new UnsupportedOperationException("Not supported.");
	}
}