documentiterators.java

MG4J (Managing Gigabytes for Java) is a free full-text search engine for large document collections

package it.unimi.dsi.mg4j.search;

/*		 
 * MG4J: Managing Gigabytes for Java
 *
 * Copyright (C) 2003-2007 Paolo Boldi and Sebastiano Vigna 
 *
 *  This library is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU Lesser General Public License as published by the Free
 *  Software Foundation; either version 2.1 of the License, or (at your option)
 *  any later version.
 *
 *  This library 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 program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 */

import it.unimi.dsi.fastutil.ints.AbstractIntIterator;
import it.unimi.dsi.fastutil.objects.Reference2ReferenceMap;
import it.unimi.dsi.fastutil.objects.ReferenceSet;
import it.unimi.dsi.fastutil.objects.ReferenceSets;
import it.unimi.dsi.mg4j.index.Index;
import it.unimi.dsi.mg4j.search.visitor.DocumentIteratorVisitor;

import java.util.NoSuchElementException;

                                                                                                                                                          
/** A class providing static methods and objects that do useful things with document iterators. */

public class DocumentIterators {

	protected DocumentIterators() {}
	
	final public static DocumentIterator[] EMPTY_ARRAY = {};

	/** An empty document iterator with empty {@linkplain DocumentIterator#indices() index set}. */
	protected static class EmptyDocumentIterator extends AbstractIntIterator implements DocumentIterator {

		public IntervalIterator intervalIterator() { throw new IllegalStateException(); }
		public IntervalIterator intervalIterator( Index index ) { throw new IllegalStateException(); }
		public Reference2ReferenceMap<Index, IntervalIterator> intervalIterators()  { throw new IllegalStateException(); }
		@SuppressWarnings("unchecked")
		public ReferenceSet<Index> indices() { return ReferenceSets.EMPTY_SET; }
		public boolean hasNext() { return false; }
		public int nextDocument() { throw new NoSuchElementException(); }
		public int nextInt() { throw new NoSuchElementException(); }
		public int document() { throw new IllegalStateException(); }
		public int skipTo( int n ) { return Integer.MAX_VALUE; }
		public boolean accept( DocumentIteratorVisitor visitor ) { return true; }
		public boolean acceptOnTruePaths( DocumentIteratorVisitor visitor ) { return true; }
		public void dispose() {}
		public IntervalIterator iterator() { return intervalIterator(); }
	}
	
	/** A singleton instance of an empty document iterator with empty {@linkplain DocumentIterator#indices() index set}. */
	public static final DocumentIterator EMPTY_ITERATOR = new EmptyDocumentIterator();
}